1.5v drop in alternator field circuit, but .5 w/o VR?

[DionR]

Why would pulling the VR connection drop my voltage loss in the charging (blue wire) circuit from 1.5v to .5v?

So here's some background:

Thought I was down to tabs and insurance before I could drive the dumb thing and all of the sudden I'm having alternator issues. End of the night one evening the amp gauge showed discharge, the next day it was overcharging. This is on a '74 Duster, BTW, with really no changes to the electrical system (stock AM radio, no electric fans or pumps, etc.), but with a aftermarket tach.

So, here's what I've done.

Multimeter showed 15.5-16v at peak between the posts so pulled the alternator (thought maybe something was grounded), swapped VR's between cars (one of which I knew was working fine), cleaned the VR connection and worked on the VR grounds. Got it down to 14.4v at peak, but that seemed too high and the gauge was about half way to the right still.

So, spent a fair amount of searching on the forum and learned lots (I am listening 67Dart273!).

So, last night I grab my multimeter (cheapy Harbor Freight thing, but better than guessing) and after turning the key on (but not starting it) I plug one lead into the (+) post of the battery and one in the back of the blue wire connector on the alternator. Bingo, 1.5 volts. Way too high, pretty sure I have a wiring problem in the ciruit and have to fix it.

I wasn't able to continue with the tests to see if the VR was grounded well as the car started and died and wouldn't fire again (out of gas, not electric related), but I did test restance between the VR case and (-) bettery post and got a very small number (which is good, right?).

I messed with the connection behind the right cylinder head and thought "hey, must be making progress" as I got .5v this time. Then I saw the VR was unplugged (don't remember why I unplugged it) and plugged it back in. Back to 1.5v drop.

Why would the VR make a 1.0v difference? Am I doing something wrong? Or is it an indication of a different problem?

 

[67Dart273]

Easy. The circuit path for the "ignition run" wire is:

From battery post -- starter relay stud -- fuse link -- bulkhead connector -- ammeter circuit -- harness splice -- ignition switch connector -- through the switch -- back OUT the switch connector on the "ignition run" (dark blue, IGN 1) back out the bulkhead connector and you are now at the engine bay side of the dark blue "ignition run wire"

which feeds.................

the ignition system

and regulator "I" terminal on 69/ older

On 70/ later this wire ALSO feeds..........

the blue alternator field......

idle solenoid if used

choke heater if used

smog doo dads on some cars.

=============================================

To simplify. In the "circuit path" I outlined above, if you simplify all of the path to.............

from battery positive .....................to engine bay side of "ignition run"

You can replace everything in between with a RESISTOR. Now the value of this resistor is going to depend on the amount of looseness and corrosion in any connections, connectors, splices, the ammeter, and the ignition switch and it's connector, and ESPECIALLY the bulkhead connector

The amount of voltage drop depends on the LOAD (current draw) on the dark blue wire.

So if you were to remove all loads, and only have "the output of the switch," it should read "same as battery."

As you add loads itemized above, the voltage drop becomes more and more. When you plug in the regulator, it adds the full field current of the alternator as well as the circuitry inside the regulator.

Your high charging voltage is likely a direct cause of this drop. The regulator "sees" this drop at it's "I" (ignition) terminal, which is the voltage sense. The regulator, assuming it's correctly set at about 14V, merely adds this 1.5V or so drop, which arrives at your 15.5 charging voltage.

If you measure the running charging voltage at say, 15.5V, and then measure from the "ignition run" terminal to ground, you will likely have 14V!!!! Proving that the regulator is doing it's job, merely the victim of low sense voltage.

===========================================

The best way to check the ground of the regulator (and ignition ECU) is NOT to use an ohmeter, but to check voltage drop directly. To do that, get the engine running at a fast idle, warm, and with battery "up" (recovered from starting.) Make the check both with all loads off, and againg with loads on, headlights, heater, etc.

Put one probe of your meter, on low DC volts, stabbed directly into the top of the battery NEG post. Stab the other onto the CASE (mounting flange) of the regulator. You are hoping for a very low voltage, the lower the better, and zero is perfect. ECU/ ignition box, same deal. More than .2V (two tenths of a volt) is too much.

============================================

Sounds like you have harness voltage drop "checked" but to be sure, check that directly with engine OFF but with key in "run." Put one meter probe onto the battery POS terminal, the other on an "ignition run" point, such as the alternator blue field lead. This should directly read the harness drop, 1.5, or whatever. Again, about .3V is the max you should read here, the lower the better.

From here it's a matter of backtracking and checking the connector terminals in the bulkhead connector, the ignition switch connector, and the switch itself. You can easily do this by making an extension lead (should fuse for safety) to clip to the battery POS terminal and one lead of your meter, long enough to reach under the dash. Now you can take your meter, again with "key in run" and check the outside / inside of the bulkhead connector, the igntion switch battery feed in and the dark blue "out." By "walking backwards" you should be able to bracket the trouble.

If you have not, this is always a good read:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

 

[DionR]

The amount of voltage drop depends on the LOAD (current draw) on the dark blue wire.

So if you were to remove all loads, and only have "the output of the switch," it should read "same as battery."

So you are saying because I removed the load of the VR, my drop went down. That makes sense.

Your high charging voltage is likely a direct cause of this drop. The regulator "sees" this drop at it's "I" (ignition) terminal, which is the voltage sense. The regulator, assuming it's correctly set at about 14V, merely adds this 1.5V or so drop, which arrives at your 15.5 charging voltage.

Got it.

The best way to check the ground of the regulator (and ignition ECU) is NOT to use an ohmeter, but to check voltage drop directly. To do that, get the engine running at a fast idle, warm, and with battery "up" (recovered from starting.) Make the check both with all loads off, and againg with loads on, headlights, heater, etc.

Put one probe of your meter, on low DC volts, stabbed directly into the top of the battery NEG post. Stab the other onto the CASE (mounting flange) of the regulator. You are hoping for a very low voltage, the lower the better, and zero is perfect. ECU/ ignition box, same deal. More than .2V (two tenths of a volt) is too much.

Yep, that was the plan. Printed out your instructions from a post in 2010 or so and planned to follow it step by step. When the car wouldn't restart and I didn't have any gas, figured I would try a resistence test and go from there. I didn't figure it was as good a test, but it was the best I could do at the time. Once I've worked my way through the harness, I will put some gas in it and do this test again.

Sounds like you have harness voltage drop "checked" but to be sure, check that directly with engine OFF but with key in "run." Put one meter probe onto the battery POS terminal, the other on an "ignition run" point, such as the alternator blue field lead. This should directly read the harness drop, 1.5, or whatever. Again, about .3V is the max you should read here, the lower the better.

Yep, exactly what I did per one of your earlier posts.

From here it's a matter of backtracking and checking the connector terminals in the bulkhead connector, the ignition switch connector, and the switch itself. You can easily do this by making an extension lead (should fuse for safety) to clip to the battery POS terminal and one lead of your meter, long enough to reach under the dash. Now you can take your meter, again with "key in run" and check the outside / inside of the bulkhead connector, the igntion switch battery feed in and the dark blue "out." By "walking backwards" you should be able to bracket the trouble.

Will do. I was just cleaning connections and then re-testing at the alternator connection. I will get a lead together instead. What size fuse would you suggest?

If you have not, this is always a good read:

http://www.madelectrical.com/electricaltech/amp-gauges.shtml

Yep, read that yesterday. Thanks!

 

[67Dart273]

Fuse is unimportant, just for safety if you were to do "arc welding" with that wire. You don't need anymore than a fraction of an amp to operate the meter, but as long as the fuse protects the wire, so 5? 10? or whatever is handy. If you have smaller, all the better.

 

[DionR]

Great! Thanks!

 

[wjajr]

When looking for voltage drop, making a hand drawn simple sketch of ignition and charging circuits is helpful. While testing list on sketch the various voltages at each connection to make keeping track of deficiencies easy, than add up the results.

 

[BillGrissom]

Excellent info above. I agree that you have too much drop thru the "ignition" circuit. It could be in the bulkhead connector, key switch, or corroded wiring. I think your 74 had the key in column, which is a pain to dig into. You might consider installing an underhood relay (standard 30 A), so the key simply actuates the relay and any drops are mute. That would give you full battery voltage to the alternator/regulator system, spark ignition system, and other "running loads". You can buy pre-wired relay base on ebay. Or you might go whole hog like 67Dart273 and I did, and install an underhood relay box from a modern car and put headlamps, horn, starter, etc on relays and get rid of the clutter of individual relays.

 

[DionR]

Excellent info above. I agree that you have too much drop thru the "ignition" circuit. It could be in the bulkhead connector, key switch, or corroded wiring. I think your 74 had the key in column, which is a pain to dig into. You might consider installing an underhood relay (standard 30 A), so the key simply actuates the relay and any drops are mute. That would give you full battery voltage to the alternator/regulator system, spark ignition system, and other "running loads". You can buy pre-wired relay base on ebay. Or you might go whole hog like 67Dart273 and I did, and install an underhood relay box from a modern car and put headlamps, horn, starter, etc on relays and get rid of the clutter of individual relays.

I'm really hoping to avoid re-wiring the car right now. Hoping to just find the problem and correct it, and save the upgrade for a later date.

Haven't spent much time on this, kind of walked away as I wanted to drop a stick of dynamite in the driver's seat and stand over it with a shotgun so no one could put the flames out. Figured as busy as the weekend was going to be it was better just to let it rest anyway.

I have traced it back to the bulkhead connector and I think it's under the dash, but I've really only spent 10 minutes or so on it since I started asking questions. At least I have a method of figuring it out, part of the frustration was feeling like I didn't have a clue how to even find the problem. Good directions 67Dart273, might have saved a car from the scrapper.

 

[67Dart273]

The diagram on the MAD page I posted above is a good overview. It doe not show the ign. switch or the path of the brown and blue through the bulkhead, but you can easily see that.

"Drop" seems to be a very repeatable and very common problem on these old girls.

Now I did a "partial" rewire on my car with a Painless harness I found on CL. I added a junkyard relay/ fuse panel out of a Voyager under the hood which gives me a source of power without any longer going through the bulkhead or a bunch of wiring. The box has fuses and relays which I've re--wired to do such things as high / low beams, ignition, fuel pump, security, etc, with at least a couple of spares.

Others have used other boxes, and Bussman puts out a box that you can "build" many different ways.

Mine is mounted on the apron behind the battery

 

[DionR]

Any pictures of it mounted?

 

[67Dart273]

That particular box, the two ears sticking out to the right have bolts going through into the outer (under) fender, just sits on top of the flat part of the apron. The two studs at the bottom of the box are the buss for 12V in. You do have to do some cutting / soldering to reconfigure the relays as you want them to hook up.

I got it cheap.

 

[BillGrissom]

Any pictures of it mounted?

I posted photos of the relay box I used (95-99 Jeep), and of the wiring in my 65 Dart, so Search my posts. Since then, did the same for my 64 Valiant.

 

[BillGrissom]

Any pictures of it mounted?

I posted photos of the relay box I used (95-99 Jeep), and of the wiring in my 65 Dart, so Search my posts. Heck, you can even see it in my Avatar, along with the Battery Brain box (blue). Since then, did the same for my 64 Valiant.

 

[DionR]

I posted photos of the relay box I used (95-99 Jeep), and of the wiring in my 65 Dart, so Search my posts. Heck, you can even see it in my Avatar, along with the Battery Brain box (blue). Since then, did the same for my 64 Valiant.

Will do. Thanks.

Not something I really want to do right now, but I will keep it in mind.

 

[DionR]

So here are some voltage drop results:

Bulkhead connection - red wire (from battery) - passenger side of the connection; .12v drop
Amp gauge red wire - .26v drop
Amp gauge black wire - .3v drop
Ignition switch power in (red wire) - .42v drop
Ignition switch power out (blue wire) - .78v drop
Blue wire to alternator at bulkhead connection - passenger side of the connection - 1.12v drop
Blue wire to alternator at bulkhead connection - engine side of the connection - 1.2v drop
Blue wire at the alternator - 1.5v drop

So, I am losing .12v in the power in bulkhead connection, .3v between the bulkhead and the ignition switch, .36v in the switch itself, .34v in the wiring from the ignition to the bulkhead, .08v in the bulkhead and .3v between the bulkhead and the alternator. Lot's of problems.

Pulled the dash wiring harness to chase the problem between the ignition switch and the bulkhead on the lead to the alternator last night. I can't see any problems in those circuits, nothing looks chewed up. I tested resistance in those circuits and am guessing that is useless because I got zip for resistance. Only things I could find that were suspect was the ground wires that screw to the dash close to the fuse box. They had been cut and spliced back together at some point in time, but they don't seem to have a good connection through the splice.

Could this be a ground issue? Is the progressively greater drop in the connections indicative of some other problem than the connections?

With the harness out I plan to clean up all of the bulkhead connections and dab some conductive grease in each one, plus fix the grounds that were cut, but other than that, I don't exactly know what to do.

 

[67Dart273]

This is not a ground problem

Example. If you back probe the power going INTO the ignition switch connector, and you read so much, let's let's say 12.6, and you measure the "run" wire coming out and it measures 12.3, you lost .3V right there in -------------- one connector terminal -- through the switch -- out the second connector terminal.

The PROBLEM is RIGHT THERE. Either one or both connectors is loose / corroded, or the switch itself is going bad, and losing power right in the switch contacts.

Another way to measure this is to measure drop directly----------put one probe on the power feed into the switch, and the other probe on the blue run wire. In the case example above, you'd measure .3V --the amount of the drop.

Now I hope you realize that drop depends on CURRENT. You are measuring this under "normal" current draw conditions, that is with the regulator, alternator field, and ignition all hooked up. If you were to UNHOOK all those components, the current draw in the circuit would be LESS and the voltage drop would appear to be LESS

So far as FIXING this I point you right back to the MAD article

Do far specifically as the "run" circuit, one way around this is to use a good quality heavy relay out under the hookd to supply ignition loads and alternator field/ regulator power.

 

[DionR]

But what about the drop between the connections? I'm getting another .34v drop between the ignition and the bulkhead on the blue wire, but there isn't a connection there other than the joint where it splits to run to the fuse box. And I get a drop at every point I can measure. I even get a .14v drop from the bulkhead to the amp gauge on the red wire, and there isn't anything on that wire.

And yes, I am testing this with everything hooked up. Not running, but hooked up and key on.

And I measured the drop on both sides of the connection at the ignition switch. Drop accross the connection is minimal, both going in and coming out.

 

[67Dart273]

The ignition wire does not go to the fuse box

I'm beginning to wonder if you are properly checking?

You say, .14 from bulkhead to the ammeter

If you are checking ON the red wire at the INTERIOR of the bulkhead, from there to the red connection at the ammeter, and you actually show .14

Under what conditions? That is what is turned on? Key? headlights? etc

Now it is POSSIBLE that the RING TERMINAL of the red wire is defective, and I have indeed found that. Examples of failed ring terminals I've found over the years are --- at the alternator output stud, at the starter solenoid, and one (forget black or red---) at the ammeter. So this DOES happen, but IS unlikely.

One way to check your work and make sure there is not some glitch in your meter or methods is to measure drop directly --both meter probes on the wire terminals--- or by first measuring one terminal to ground, then measuring the second to ground and subtracting. The two results should be the same.

 

[DionR]

The ignition wire does not go to the fuse box

I agree, the brown ignition wire does not split, but the blue wire that runs to the alternator and VR does split and run over to the fuse box. That's the one I am talking about.

I'm beginning to wonder if you are properly checking?

I'm using the method you suggested, with a lead from the positive battery terminal to my multimeter and the the other lead on the connection. The first section on my second post this morning showed the observed voltages shown on the multimeter at each connection as listed. The paragraph after that was my math showing the drop between each connection.

Here are the observed voltage drops at each connection:

Red wire at bulkhead connection, passenger side - .12v drop
Amp gauge red wire - .26v drop
Amp gauge black wire - .3v drop
Ignition switch power in (red wire) - .42v drop
Ignition switch power out (blue wire) - .78v drop
Blue wire at bulkhead connection, passenger side - 1.12v drop
Blue wire at bulkhead connection, engine side - 1.2v drop
Blue wire at the alternator - 1.5v drop

You say, .14 from bulkhead to the ammeter

If you are checking ON the red wire at the INTERIOR of the bulkhead, from there to the red connection at the ammeter, and you actually show .14

No, the .14v drop is my math. I show .12v drop at the red wire on the interior side of the bulkhead connection and .26v drop on the red wire at the amp gauge, using the above method with a lead direct from the positive battery post.

Under what conditions? That is what is turned on? Key? headlights? etc

Key in the run position, radio/head lights off. No dome light either.

Now it is POSSIBLE that the RING TERMINAL of the red wire is defective, and I have indeed found that. Examples of failed ring terminals I've found over the years are --- at the alternator output stud, at the starter solenoid, and one (forget black or red---) at the ammeter. So this DOES happen, but IS unlikely.

I will look into that.

One way to check your work and make sure there is not some glitch in your meter or methods is to measure drop directly --both meter probes on the wire terminals--- or by first measuring one terminal to ground, then measuring the second to ground and subtracting. The two results should be the same.

Will do, after I put it all back together.

 

[67Dart273]

Red wire at bulkhead connection, passenger side - .12v drop
Amp gauge red wire - .26v drop
Amp gauge black wire - .3v drop
Ignition switch power in (red wire) - .42v drop
Ignition switch power out (blue wire) - .78v drop
Blue wire at bulkhead connection, passenger side - 1.12v drop
Blue wire at bulkhead connection, engine side - 1.2v drop
Blue wire at the alternator - 1.5v drop

Key in the run position, radio/head lights off. No dome light either..

It SOUNDS like you are checking correctly, but with only that ignition load, that is one HELL of a lot of drop. A big drop "out" of the ignition switch might be expected, as in a bad connection, bad switch, but that much at the ammeter and to the sw is a bunch with no more current than should be drawn

You're right --the dark blue branches off and feeds the fuse box, I'd forgotten about the change in later models. That fuse feeds the cluster power, the seat belt interlock, and some options if equipped.


I sent you a PM.

 

[DionR]

Bringing this back up because I still can't get it solved.

I've swapped the engine compartment harness, pulled the dash harness to check for bad wires and cleaned connections, changed the battery (which got the amp gauge functioning correctly), plugged a different ignition switch in, bypassed the amp gauge, ran a jumper wire around the bulkhead connection to the amp gauge connection, checked grounds, changed the ignition box, had the alternator tested and replaced the voltage regulator with a new one. I'm sure there are things I've forgotten, but it feels like I have done just about everything I can but still have a massive voltage drop at the alternator connection.

At least in my mind (I'm way past thinking I might have something figured out, every time I do I get slapped), I think I have eliminated a power supply or connection problem.

So, is it possible that I have a huge amp draw that is showing up as a voltage drop? Is it possible that something is pulling too much power and showing up like that? Can the alternator go bad in this way? Haven't unplugged the coil yet either, maybe the coil is drawing a bunch of amps?

Currently the car has the dash harness just laying there with the ignition switch plugged in and the main engine harness connected (power in and ignition wire out) and the amp gauge connections bolted together with a small screw. No gauges, and the radio, etc. are not powered, no headlights, no taillight harness, or anything else. Only what is on the harness (buzzers, blinkers, fuse box and seatbelt interlock).

This car is about to go on the block and get sold if I don't figure this out soon. Starting to think I would rather mess with an SN95 Mustang than screw around with this anymore. Tired of this thing kicking me in the nuts.

 

[67Dart273]

OK you lost me. What exactly do you have hooked up and on what circuit, and "what" is the trouble?

If you are talking about the ignition feed, there's only so much "on" that and it varies from car model and car year

IGN1 or "run" supplies

ignition circuit, IE ECU

VR

choke heater if used

Various smog junk on some cars

Refer to the shop manual section 8. There's a procedure in there to measure alternator field current draw. Some of the newer, heavier alternators draw more, up around 6A I think.

With the harness laid out like that it should take very little time to find.........

 

[DionR]

OK you lost me. What exactly do you have hooked up and on what circuit

I have the ignition switch, misc. buzzers, flashers (whatever comes out with the harness) and the seat belt interlock box (so I can start the car) and the middle plug of the engine harness connected to the the dash harness. Nothing else is connected. Pretty much the absolute minimum to start the car.

"what" is the trouble?

15.5v across the battery posts due to a 1.5v drop at the alternator field plug (blue wire). Started with an amp guage that wouldn't return to zero, but the newer battery seems to have solved that. As stated above, I have increasingly large voltage drops as I move farther along the harness out towards the alternator and despite my best efforts (over a freaking year and a half time span), NOTHING has changed.

If you are talking about the ignition feed, there's only so much "on" that and it varies from car model and car year

IGN1 or "run" supplies

ignition circuit, IE ECU

VR

choke heater if used

Various smog junk on some cars

Only things plugged into the IGN 1 leaded out of the firewall is the ballast resistor, ignition box, coil, alternator and VR. Everything else is unplugged.

 

[67Dart273]

OK I would start "as if you" were starting over.

First with things hooked up in the igntion / charging circuit recheck the harness drop, that is, from the ignition switch to the VR.

Something you MAY be missing..........Maybe the VR connector is corroded or loose, don't discount that. I HATE using pins but sometimes they are necessary. You can "stick" a small pin through the blue VR wire right at the VR plug. Check between there and battery POS with key on See what your drop is. Make sure both ignition, and VR / alternator field are hooked up, and any other loads normally on the ignition circuit.

Don't forget the "wiggle" test. Wiggle the VR connector, the bulkhead connector, the IGN switch connector and the switch itself.

============================================================

MAY BE a repeat. Another check would be to "jumper" (testing) some of the harness. Find the junction of the ignition run wire. This can be the bulkhead connector terminal, or at the coil resistor if still used. With the engine running "fast idle" and while monitoring battery voltage, confirm that it is over voltage.

Then "probe" a jumper wire from battery + to the ignition junction. If battery goes "to normal" (14V) you are on the track and it's still in the harness / switch / connections

=======================================

MIGHT be the battery. Try to borrow a known good battery and swap in

=======================================

REcheck NEGATIVE (ground) drop between battery NEG and VR ground

=======================================

If none of the above is the problem replace the VR

 

[DionR]

OK I would start "as if you" were starting over.

First with things hooked up in the igntion / charging circuit recheck the harness drop, that is, from the ignition switch to the VR.

Something you MAY be missing..........Maybe the VR connector is corroded or loose, don't discount that. I HATE using pins but sometimes they are necessary. You can "stick" a small pin through the blue VR wire right at the VR plug. Check between there and battery POS with key on See what your drop is. Make sure both ignition, and VR / alternator field are hooked up, and any other loads normally on the ignition circuit.

Don't forget the "wiggle" test. Wiggle the VR connector, the bulkhead connector, the IGN switch connector and the switch itself.

============================================================

MAY BE a repeat. Another check would be to "jumper" (testing) some of the harness. Find the junction of the ignition run wire. This can be the bulkhead connector terminal, or at the coil resistor if still used. With the engine running "fast idle" and while monitoring battery voltage, confirm that it is over voltage.

Then "probe" a jumper wire from battery + to the ignition junction. If battery goes "to normal" (14V) you are on the track and it's still in the harness / switch / connections

=======================================

MIGHT be the battery. Try to borrow a known good battery and swap in

=======================================

REcheck NEGATIVE (ground) drop between battery NEG and VR ground

=======================================

If none of the above is the problem replace the VR

I check the voltage drop every time I make a change, and it doesn't get any better.

I've replaced the battery with a known good one.

I've replaced the VR with a new one.

I've checked the grounds, repeatedly and don't find anything amiss.

I think the next thing to get replaced is the car. :banghead: