question on bulkhead connector bypass

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Dave NEO

Dave NEO

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In this discussion they basically talk about jumping the starter relay with the alternator stud - my question is: is it obvious which stud on alternator to connect to? - '68 383 with original style alternator. thnx for any comments. Also can you leave amp gauge alone or do you have to disconnect ?

1. Bulkhead (firewall) are the universal trouble spot. Left, connector used on ‘71-‘74 B-bodies and all E-bodies. Charging system current (to ammeter) typically utilizes cavities 16 and 18. On pre-‘70 B-bodies and ‘67-mid-‘75 A-bodies, ammeter current is typically via cavities J and P. These are the trouble spots. Note that on fleet vehicles, the factory wisely routed charging though a solid wire passed through a grommeted hole in the firewall, eliminating the trouble spot.

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3. Here’s where those firewall wires terminate - the ammeter on the instrument cluster. Notice how beefy the studs and wiring are. Wouldn’t it be lovely if the bulkhead connector was this good? Notice that the “black” (negative) side of the ammeter was the factory’s choice for accessory current take-off.

4. To straighten out the wiring problem permanently, you need some decent supplies. A few feet of automotive-grade wire, 10 or 12 gauge (depending on you alternator’s rating and anticipated current loading), fusible links (see text), some crimp splices and heat-shrink tubing, and, if need be, some quality electrical tape. If you’re adding any other accessories, do yourself a favor and opt for the modern blade-type fuse holder and fuses.

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5. Connect a fusible link to the starter relay stud. Crimp-splice in a piece of suitable (heavy-gauge) wire, and connect the other end to the alternator stud. That’s it....firewall problems bypassed forever!

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You need to post the source where you got this from. There are a couple or more ways to do this. There is the MAD article which some criticize. It is one way, and if nothing else, the MAD article gives a great overview of how these girls work and why the trouble exists and comes to be

Crackedback markets a simple bypass cable. Look him up
 
Dave NEO said:
In this discussion they basically talk about jumping the starter relay with the alternator stud - my question is: is it obvious which stud on alternator to connect to? - '68 383 with original style alternator. thnx for any comments. Also can you leave amp gauge alone or do you have to disconnect ?
Click to expand...

Well you can leave it there but what you are doing with this is bypassing it, and will no longer function.

The big trouble spots in these girls in no particular order are:

The bulkhead connector mostly the big red and big black ammeter wires

The ammeter connections and the meter itself

In rare cases the under-dash welded splice

The headlight switch and connector

The headlight feed throughs through the bulkhead connector

Sometimes the ignition switch connector, and sometimes the switch itself

As Redfish has pointed out many times, on the later cars with the "white" engine harness connector, that should be bypassed.........the only white connector in the engine bay
 
The alternator terminal you connect to would be the big one with the 1/4 (?) bolt with the nut on it. The above described process only solves part of the problem. It only reroutes the alternator charging current. All the current to run the car electrical system still goes through the bulkhead connections. The ampmeter can stay connected, but it will read “discharge “ all the time because the charging current doesn’t go through it any more, rendering it useless
 
OK thanks - yes I understand the ammeter will not be correct- no prob I have other gauges including a voltmeter anyway. I see now it has to be the BAT terminal on the alternator to jump to the starter relay. That should reduce draw though bulkhead connector when starting, no?
Source was this:
Vintage Chrysler electrical repairs and updates

BTW I put relays in some time back for the headlights which I hope has reduced load through bulkhead connector also. I have no radio or other big power draws besides heater fan (which I never use) and pretty much just the convertible top power, interior and running lights. I'm in process of taking apart and cleaning the 3 plugs in the bulkhead connector. They look pretty decent so far.
 
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Make sure you grease ‘em up good when you put them back together. The other wire that gives people trouble is the ignition 1 wire, you might look at it carefully, or just pull out the lugs and run a wire straight through the cavity.
 
Mike69cuda said:
The alternator terminal you connect to would be the big one with the 1/4 (?) bolt with the nut on it. The above described process only solves part of the problem. It only reroutes the alternator charging current. All the current to run the car electrical system still goes through the bulkhead connections. The ampmeter can stay connected, but it will read “discharge “ all the time because the charging current doesn’t go through it any more, rendering it useless
Click to expand...

This statement might be somewhat misleading. "All the current to run the car" is not nearly as much as "all the current to run the car" PLUS charging current which is what "it used to be." So even if the bulkhead/ ammeter is in somewhat damaged shape, bypassing from the alternator output to the starter relay will relieve the bulkhead circuit of a LOT of load.

It is IMPORTANT (to the OP) to make sure such a bypass has some sort of fuse / fuse link/ breaker because if the alternator shorts, you now have NO protection if you do not



[
 
Cool - that's what I was hoping for and wanted to be sure of. Great info always here - thnx.
 
Installed bypass and working fine - one difference I notice is at idle I get quite a lot of flickering in headlights and dash I did not really have much of before - my volt gauge shows voltage up and down at idle like the lights, steadier at higher rpm.. Is this common with the bypass set-up? I guess I don't care as long as it's gone at higher rpms but appreciate any comments/tips - thanks. btw, got electronic ignition if that could be an issue. I had already put in some headlight relays that basically let them run direct off battery and had gotten used to bright and virtually no flicker headlights at any RPM but that may be gone if I stick with this bypass setup.
 
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maybe we are bypassing the voltage regulator and the output direct from alternator to starter relay, lights and battery is not as steady as a result? Not sure that makes sense -any one that understands charging system maybe shed some light here. thanks. otherwise may have to lose this bypass set-up. was worth a shot.
 
What is likely happening now......and this is VERY common, is the voltage drop problem in the harness. There is a couple of issues. "What you fixed" when you did the ammeter bypass is you upgraded the charging output wire of the alternator, and the supply to the electrical loads in the car........headlights, heater, etc

BUT SOME OF THIS STILL comes back through different terminals of the bulkhead connector. ONE of those is the (normally) blue "ignition run" (IGN1) wire which comes FROM the ignition switch and supplies power under the hood to ignition, some smog devices, the electric choke if used, AND THE VR and alternator field

IF THERE IS voltage drop in that circuit the battery will overcharge, and if the connections are not stable, the flickering will result

HOW TO CHECK:
1...GROUND:
There is actually one MORE possible path that causes this, and this is the grounding relationship between battery, body, engine, and voltage regulator

TO CHECK, run engine until warm and battery is "normalized." Run engine to simulate "medium cruise" RPM. Run this check first with all loads turned off, and again with them on (heater, lights, etc)

Stab one probe of your meter into the top of the NEGative battery post. Stab the other into the mounting flange of the VR. Be sure to get through paint, rust, etc. You are hoping for a very very low reading, the lower the better, and zero is perfect

2......HOT SIDE of the harness:

To make this check turn the key to "run" with the engine stopped. Leave all wiring connected as "normal." Connect your meter to as close as you can to the VR ignition terminal. This would be the "key" side of the ballast resistor, where the two wires are jumpered together if you have a 4 terminal ballast. Otherwise, probe from there to ground and find the HIGHest reading. Then leave one probe of your meter hooked there

Then, stab your remaining meter probe into the POSitive battery post. You should read a very low reading the lower the better. ANY reading here is ADDED to the charging voltage set by the voltage regulator. If your read more than say, .3V (3/10 of one volt) you need to find the problem

They are in no particular order: the bulkhead connector terminals, the ignitions switch connector, the switch itself, and on newer cars, THE WHITE underhood ignition harness connector.

One way "around" thsi is to cut (electrically) the blue "ignition run" (ign1) wire coming out of the bulkhead and into the engine bay. Use the bulkhead connector end to activate a relay, and feed the relay contacts from the start relay "big stud." Connect the underhood end of the cut blue wire to the switched side of the relay contacts. This will provide a good direct path from the VR to the battery
 
I noticed with the by pass in place and head lights on, my handheld voltmeter showed the alt output was almost 14v - it was lower 13's w/o the bypass connected. Is that suggesting the overcharging you mentioned?
 
nevermind - I answered my own question - of course this 'by-pass' will result in overcharging the battery because it essentially bypasses the VR which would otherwise open and close the charging circuit to allow charging current to battery only when required to maintain preset minimum voltage, duh. I'm thinking this by-pass is just not a great idea. Anyway, having cleaned the wires in the bulkhead connectors and replacing the fusible link in there, I'm more confident the original set-up will continue do it's job; worked pretty good for 50 years. Thanks for all your input/suggestions.
 
they instructed to run it from alternator to the starter relay stud which connects to battery so VR not involved in that.

5. Connect a fusible link to the starter relay stud. Crimp-splice in a piece of suitable (heavy-gauge) wire, and connect the other end to the alternator stud. That’s it....firewall problems bypassed forever!
 
Dave NEO said:
nevermind - I answered my own question - of course this 'by-pass' will result in overcharging the battery because it essentially bypasses the VR which would otherwise open and close the charging circuit to allow charging current to battery only when required to maintain preset minimum voltage, duh. I'm thinking this by-pass is just not a great idea. Anyway, having cleaned the wires in the bulkhead connectors and replacing the fusible link in there, I'm more confident the original set-up will continue do it's job; worked pretty good for 50 years. Thanks for all your input/suggestions.
Click to expand...

Please allow me to jump in here for a quicky.
What happened by doing the bypass is that you have taken some of the load off the harness, and therefore reducing the needed voltage.
Your charging voltage was more steady because of the load it was compensating for, and now without that constant load on things the regulator gets a bit jumpy.

This in no way changes what Del says, but just an explanation of why it does it.
14v isn't overcharging, but more where it should be in my opinion.
Just so you know, the regulator senses the voltage from farther inside the harness with that blue wire off the regulator plug, so it's still sensing.
The lowered load on the electrical system from the bypass and the use of headlight relays cause this to happen.
Some of us bypass the harness connection of the blue regulator wire and run it direct to the battery+ starter relay terminal with it's own relay inline so it gets a direct sensing of the battery voltage without going through the rest of the harness and getting "tricked" into erratic operation.
This way when you turn on your key and the relay closes the regulator see's actual battery voltage.

And again, Del's advice still stands, I just thought different wording might help you realize why you are now seeing what you are.
 
That does clear up a few things for me thanks but that does not seem to explain how the VR can reduce charging current to battery when it needs to to prevent overcharging if there is a constant direct charging current to the battery from the alternator via the the starter relay connection.
 
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If I read you correctly, sounds like I can try detaching the blue wire from the VR that goes to harness and attach another wire to the VR that will run with a relay in line to the starter relay. If you know a recommended relay for this I suppose I 'd give it a try.
 
Dave NEO said:
That does clear up a few things for me thnks but that does not seem to explain how the VR can reduce charging current to battery when it needs to to prevent overcharging if there is a constant direct charging current to the battery from the alternator via the the starter relay connection.
Click to expand...

The VR senses system voltage and varies the field voltage to regulate the alternators output, so just because there is a direct wired connection from the alternator battery stud to the battery doesn't mean it's charging the battery at full output.
How much voltage the field wire (usually green) on the back of the alternator puts into the alternator determines the alternators output.
Normal charging output of the alternator is between 13.8 and 14.2 so you are well within the normal and on the right track to having a nice stable electrical system.

Try running all lighting for the dash, interior and outside lighting besides headlights with LED and watch your electrical systems response.:D
I run with at least my parking lights on to give the charging system something to do besides keep up with the load of an old electrical system with under gauged wiring and the voltage losses from it AND charge the battery.
In return I get headlights that don't dim when idling at a stop light, as well as wipers and blinkers slowing, heater blower and other electricals have all the power they need to always work the same no matter rpm's.

Just saw your last reply.:D
Yes, a relay helps a lot on the sense wire.
 
"The VR senses system voltage and varies the field voltage to regulate the alternators output, so just because there is a direct wired connection from the alternator battery stud to the battery doesn't mean it's charging the battery at full output."
OK -that helps big time as I did not know that whatsoever and that is main issue I was stuck on. So should I try other mod with regulator wire to the the starter relay stud? Just need to know what type relay to go after. thnks again all for patience with my questions. .
 
Dave NEO said:
That does clear up a few things for me thanks but that does not seem to explain how the VR can reduce charging current to battery when it needs to to prevent overcharging if there is a constant direct charging current to the battery from the alternator via the the starter relay connection.
Click to expand...

An easy way to tell how it would work is to run a wire direct from the battery+ to the blue on the regulator with the car running.
That would temporarily make that direct connection to the battery+ for the sense wire and show you what difference doing it with a relay would make before you go to all the trouble of doing it to find it made very little difference.

On my car it helped a lot, but it doesn't always.
 
not a lot of trouble really - I'm damn good with wires, just don't know where to put'em..!

what sort of amps for relay?
 
Dave NEO said:
not a lot of trouble really - I'm damn good with wires, just don't know where to put'em..!

what sort of amps for relay?
Click to expand...

It only needs to be making the contact so amps don't really matter that much.
I sometimes use relays out of cars or trucks in the wrecking yard for low draw things like this, but they are even overkill for something like the sense wire.
The under hood fuse panels on newer cars and trucks are loaded with them, and most made in Canada instead of China.
To buy one, 5 or less amps duty is plenty, but it could be a 30amp and it won't matter.
 
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