Voltage problems, cutting out when hot

[mopower76]

I am hoping you guys may be able to assist me with the charging problems I’m having with my 1974 Dodge Dart Sport.


I did the parallel wiring as detailed in older posts as I have on all of my B and E Bodies, I went through all of the wiring harnesses in the car and made repairs where needed (really in good shape for a rat infested desert car)

I’m running a 1998 360 Magnum with original serpentine front drive from truck. It has a new replacement alternator that I believe is a 90amp.


What brings me to the question at hand is when driving after the car gets up to temperature it starts cutting out hard under acceleration, at idle it seems ok but not exactly right.

This led me to replace the coil, orange box and adding the .5 ballast.

Drove again with the same results, when cold it runs fine, once hot (normal opp. Temp) it cuts out hard under moderate acceleration.

This led me to test readings at the coil, (coil so hot you can’t touch it) relay and add grounds everywhere. (IGN. Box, volt reg. Block to body


I am running dual fans on dual 70amp relays with Dakota Digital PAC-2750 controller, ac is not hooked up as yet.

Pro-Comp distributor, MSD blaster .8 ohm coil with .8 ballast in conjunction with the OE 5.0ohm ballast (original 4 pin ballast), new Packers 8.0mm low resistance plug wires, MP orange box. New voltage regulator.


Before doing the parallel wiring to the amateur the gauge was reading over charge all the time with alternator output being 15.5 V and battery showing 15.4 V.

After running the parallel wiring ( eight gauge wire from alternator to ammeter and 10 gauge wire from amateur to starter relay lug with 14 gauge fusible link ) the gauge now reads large discharge at startup then quickly recovers and sits just under the center line as if it is now discharging slightly at idle. As soon as it gets up to temperature the fans kick on and it hits discharge fairly hard, not fluctuating and not buried but at the second line on the gauge.

Here are pictures of Volt readings at different areas and see if there is anything I am missing.

As stated above, I’ve done this in the past without problems and removing the fans from the equation does not make a difference. (Except for readings when they do run)

Thanks for any advice in advance as always.

Running at batt

Running at alt

Not running, key on +

Not running key on -

Key on

Key on

Key on

Key on

Key on not running

 

[Mattax]

It sounds like the fans & other equipment are tied in to the batter side of the ammeter.
If you're going to use the ammeter, only thing hooked to that side of it should be the battery.

Constant heavy charging

No power in the car

 

[67Dart273]

You need to label each photo to show what it represents. The 15.71 is obviously running charging and that is too much You sure the extra ballast is wire correctly?

If you are still running an ammeter, where are the fans pulling their main power?

 

[mopower76]

You need to label each photo to show what it represents. The 15.71 is obviously running charging and that is too much You sure the extra ballast is wire correctly?

I did label under each picture, I can be more specific if needed.

If you are still running an ammeter, where are the fans pulling their main power?

When I remove the power to the fans, there is no change in voltage just as when they are not running voltage readings are the same.

Fan main power is fed at the starter relay, I thought about rerouting to the lug on the alternator instead of the starter relay.

I wired the fans as was laid out in another post on adding Ford Contour dual fans with dual relays and DD controller.

 

[mopower76]

The extra ballast should be wired correctly, I’ll retrace the wires to be sure. All I did was flip the connectors upside down using the correct pins/sides and used jumpers to the new .8 ballast.
Again, I will trace wires and get back. Should be pretty straight forward.

 

[Mattax]

Fan main power is fed at the starter relay, I thought about rerouting to the lug on the alternator instead of the starter relay.

On the alternator side is the only way that makes sense.
The purpose of the factory ammeter is to show the amount of charging or discharging of the battery. If additional equipment is placed on the battery side, then the ammeter readings won't be very useful.

When I remove the power to the fans, there is no change in voltage just as when they are not running voltage readings are the same.

Voltage is potential. Assuming the power source can provide the amount called for, the system voltage won't change.
An ammeter shows flow.

The extra ballast should be wired correctly, I’ll retrace the wires to be sure. All I did was flip the connectors upside down using the correct pins/sides and used jumpers to the new .8 ballast.

The ballast resistor should be matched to the coil and to a lesser extent the ECU.
P-part orange box and Blaster 2 is probably should have either .5 Ohms or .8 Ohms resistor in circuit branch directly feeding the coil. Not both.

 

[Mattax]

Voltage is potential. Assuming the power source can provide the amount called for, the system voltage won't change.
An ammeter shows flow.

If we were talking about a compressed air system or piped water in your house the analogy is this.
The pressure in the pipes is the voltage.
The water (or air) flowing is the current.

If every faucet in your house is shut, the pressure through all the supply lines is the same as the source. If just one faucet is opened, hopefully the pressure doesn't drop even though water is flowing in that line.

Lets say the house has a well and water tower. The well pump when running can supply 14.5 psi and up to 60 gallons per minute. The water tower is only high enough to supply 12.5 psi, but has 400 gallons in it.


So on a factory setup, (no fans, no extra anything) all of the main circuit should be at the same voltage.
The ammeter shows flow to or from the battery. Once the battery is charged, the ammeter line should have zero current flowing through it.

If a wire has been added in parallel from the alternator to the ammeter, then when the alternator is running, current can flow through either or both.
It will take the path of least resistance.

If the battery is taking a charge and other equipment is being run, very likely some current will run through both.

Using the same example but with fans or other electric devices attached to the starter relay, the ammeter shows current flow for either or both charging and the fans.
Even with parallel wires, such an arrangement is putting constant loads and will have higher peak loads on the ammeter. It was really only intended for relatively short term loads. Same with the fusible links.

 

[Mattax]

15.7 Volts is a problem.
Most likely the regulator is getting wrong information (low voltage).

What the 5.9 and 10.9 V are showing we can only guess. Labels and/or diagrams would be a big help.

 

[mopower76]

The 5.90 and the 10.19 volt are measurements taken from either side of the MSD .8ohm ballast with the key in the on position, engine not running.
The two pictures that follow are being taken from the 5.0ohm side of the factory 4 pin ballast in the same manner, key on engine off.
And yes, one of my main concerns is in fact why (or where/what) is the VR getting the wrong information...
Thank you for the well laid out explanation and graphs.

 

[Tooljunkie]

I have seen batteries that cause a car to stall while cornering hard. Loose plates.
Perhaps not the case here,but a battery swap is pretty easy.

 

[Mattax]

When current flows through a resistor, or any device, the voltage drops.

 

[Mattax]

The 5.90 and the 10.19 volt are measurements taken from either side of the MSD .8ohm ballast with the key in the on position, engine not running.
The two pictures that follow are being taken from the 5.0ohm side of the factory 4 pin ballast in the same manner, key on engine off.
And yes, one of my main concerns is in fact why (or where/what) is the VR getting the wrong information...
Thank you for the well laid out explanation and graphs.

A '72 has two big differences from a 60's type scheme shown above.
Voltage regulator.
Controls the rotor's connection to ground (green wire) based on voltage in the blue wire. Think of the blue wire as a voltage sensing wire. No appreciable current flows into the VR from the blue wire.
Ignition Switch
Additional connector for all the wires to and from the switch because its in the steering column.
ECU ?
Some '72 cars may have had a Chrysler ECU, but I'm assuming here that the ECU wiring was added. A factory ECU from the time would have two resistors and 5 wires.
The power for the ECU can be tapped from any location on the run circuit. In the below illustration its shown as a splice.

 

[RedFish]

A ballast resistor creates voltage drop. So 12 or 13 in = 7 or 8 out. Your pics show 10.X in and less than 6 out to coil. will your coil function properly on 6 volts? In theory, if you're loosing voltage between the battery and ignition system, the charging system is suffering low voltage too. In most case both are fed by the same blue wire from ignition switch. So 10.X at resistor would be 10.X at voltage regulator also.

 

[67Dart273]

The 5.90 and the 10.19 volt are measurements taken from either side of the MSD .8ohm ballast with the key in the on position, engine not running.
The two pictures that follow are being taken from the 5.0ohm side of the factory 4 pin ballast in the same manner, key on engine off.
And yes, one of my main concerns is in fact why (or where/what) is the VR getting the wrong information...
Thank you for the well laid out explanation and graphs.

What do you have from the key switch? Functional path is power to ignition switch---out of the switch on "ign1" (ignition run)---through the bulkhead connector,---and to one side of the ballast. If you can't find that wire, disconnect at least 3 of the ballast wires and look for the only one which has power. Note that, hook everything back up, and measure that point---key in run--engine stopped

 

[mopower76]

A '72 has two big differences from a 60's type scheme shown above.
ECU ?
Some '72 cars may have had a Chrysler ECU, but I'm assuming here that the ECU wiring was added. A factory ECU from the time would have two resistors and 5 wires.

View attachment 1715370660

The car in question is a 1974 so it came factory with the 5 pin ECU.

What do you have from the key switch? Functional path is power to ignition switch---out of the switch on "ign1" (ignition run)---through the bulkhead connector,---and to one side of the ballast. If you can't find that wire, disconnect at least 3 of the ballast wires and look for the only one which has power. Note that, hook everything back up, and measure that point---key in run--engine stopped

Thank you for the idea, I’ll check at the switch as soon as I can get back out there.
First and foremost I’ll be doing away with the fans in the circuit all together for testing then I’ll be switching fan power to the alt side of the charging system.

I have seen batteries that cause a car to stall while cornering hard. Loose plates.
Perhaps not the case here,but a battery swap is pretty easy.

I replaced the battery with a new battery (2 months old) and had a local shop load test the battery in the car, it tested good.
Again, I appreciate all of the input.

 

[mopower76]

And again Mattax, thank you for the great input and schematics.

 

[Mattax]

The car in question is a 1974 so it came factory with the 5 pin ECU.

OK. 67Dart273 has probably given you the most direct way to identifying the power feed.

If you are looking in the '74 FSM, it probably has a wiring diagram like the '73. This is snip from the '73 so details may not be exactly the same.

Here's how you decipher it.
J is the Ignition circuits.
J2A is ignition power feed when key is in run position. 16 DBL is 16 gage Dark Blue. The original ECU got power in run through J4 through a 5 ohm resistor.
A more recent ECU will get all power simply through J2E.

If we follow J2C back, not shown in the snippet above is an oval marked CE2 N
The ovals marked CE are connectors, and the key for them is several pages later. CE2 is the bulkhead connector. N is the cavity. So the blue with white trace is the power feed when the key is in run position.

 

[mopower76]

It looks like the schematic is the same as 74.

With the key on engine off I’m getting 11.65v at the J2A pin at the ballast.

Am I correct in assuming that since I’m running an orange box (4 wire) that J4 is not being used therefore I can eliminate the 5ohm ballast resistor from the 4 pin and only use (with correct sides of the plugs) the MSD .8 and ditch the 4 pin ballast all together?

This is what I was actually hoping to do as I knew there was a difference in the 4 and 5 pin ECM’s but couldn’t find (figure out on my own) how the circuits worked.

You guys are what makes this sight an invaluable resource for guys like me.
Mattax, if your knowledge was gold you’d be a Bazillionaire!

Again can’t thank all of you enough! I think this should let me get back to where I need to be.

On another note I pulled all the wires from the alternator started the car and took a reading which read 0.00V.
I’m going to pull it off and have it tested.
Again I have no idea what this actually means but thought I would run it past you guys and get an opinion since it is overcharging (15.77v when hooked up.
(I’m jumping ahead, I know I need to get the ignition and other wiring sorted before concentrating on the alternator.)

 

[mopower76]

And getting 11.65 at blue with white tracer at the ignition switch. Key on engine off.

 

[mopower76]

12.59 at blue whit tracer at bulkhead

That’s at bulkhead with charge harness unplugged from bulkhead.

FYI - fans are completely out of charging system and testing without alternator hooked up. Key on not running.

 

[mopower76]

So doing more probing I found that with the ignition switch unplugged testing at each pin there is 12.x (same as batt) at the blue pin to bulkhead and 11.x at the yellow pin in the same connector.
I traced that wire to the bulkhead connector, disconnected (again) and tested the yellow wire from the unplugged connector and it reads the same 11.x then traced it to the starter relay where it reads 11.x with the ignition switch still unhooked.

Ignition switch hooked up and key off

Key on (not running)

Ignition switch unhooked

So with the yellow wire unhooked at the starter solenoid that terminal reads about the same... isn’t this terminal supposed to only have voltage at start?

 

[67Dart273]

Something is haywire. You are talking about unplugging the switch and reading voltage. You are getting this on the bulkhead end of the harness and not the connector on the ignition switch end? That wire should be dead

But further, may not tell you anything to probe with various harness parts disconnected.

"Let's say" you have a poor contact in the ignition switch or in the switch connector in the "run" circuit, example.

If you read that voltage at the switch connector, everything connected normally, the CURRENT DRAW of the loads connected to it will cause a low reading and alert you.

But if you take the same reading with the loads/ connector unhooked, it may well read "normal."

If you have the switch disconnected........and are reading the connector half that leads to the bulkhead.......and if you showing voltage on either the yellow start wire or the blue run wire...........something is feeding back there someplace, possibly the fans??

 

[67Dart273]

Your descriptions are confusing me. Last photo............You are measuring the yellow wire at the starter RELAY? And this is with the key OFF?

Beginning to look like a bad igntiion switch to me

 

[mopower76]

Fans are completely removed from charging/wiring

Something is haywire. You are talking about unplugging the switch and reading voltage. You are getting this on the bulkhead end of the harness and not the connector on the ignition switch end? That wire should be dead

But further, may not tell you anything to probe with various harness parts disconnected.

"Let's say" you have a poor contact in the ignition switch or in the switch connector in the "run" circuit, example.

If you read that voltage at the switch connector, everything connected normally, the CURRENT DRAW of the loads connected to it will cause a low reading and alert you.

But if you take the same reading with the loads/ connector unhooked, it may well read "normal."

If you have the switch disconnected........and are reading the connector half that leads to the bulkhead.......and if you showing voltage on either the yellow start wire or the blue run wire...........something is feeding back there someplace, possibly the fans??

At the ignition switch wiring plug going to the bulkhead the yellow wire reads-

So I’m now I’m going to throw a monkey wrench into the entire process.
I hadn’t given this too much thought because I was assuming I had it bypassed as shown in another forum.

This car has the dreaded 1974 seatbelt safety system... there is a box under the hood and another (green) under the dashboard.

The yellow wire at the starter relay reads 11.x unplugged with the ignition switch unplugged as does the brown wire (neutral safety switch)

 

[mopower76]

I’m sure this is my source of every problem...I apologize for not stating this from the start. The car has been starting so I didn’t give it a second thought until now...

Now where the Funk do I start????

I realize this is a complex system that is not easily eliminated without replacing the entire under dash harness and under hood wiring harness.

Again I’ve read in other postings that you can bypass the interlock system simply by making a jumper wire between the two yellow wires at the interlock reset button under the hood.
Obviously there is something more going on somewhere in this system.