Burnt wires at Bulkhead connector

[HWYCRZR]

As I was cleaning up my harness (68 Polara), which thankfully is out of the car and on the workbench, I see some melting on a couple of my main power supply wires at the bulk head connector. I found a new replacement bulkhead, and am changing it out, but am wondering the root cause.
This is the circuit which runs through the J and P terminals on the bulkhead connector.
Circuit starting in the engine bay:
Battery + A1A-10-R through Starter relay (also branches to horn relay and Starting motor) through A1B-10R to connector. Connects -A1C-16-DBL fusible link to J terminal on bulk head disconnect engine bay.
Bulkhead disconnect Dash -J terminal (signs of melting)- A1-12-R to Ammeter terminal 1 (Q1-12-Rto Accessory Circuit Breaker also connects to this terminal)
From Ammeter terminal 2 - R6A-12-BK (left terminal) - to splice / connector going 4 places(would also provide power for clock if equipped)
-Wire 1 from splice - R6-12-BK to P terminal (signs of melting) on Bulkhead connector - P terminal R6-12-BK to Alternator BAT terminal
-Wire 2 from splice- J1-12-R Feeding the Bat terminal on Starter switch
-Wire 3 from splice - L1-16-BK feeding Headlamp Switch B1
-Wire 4 from splice - Q3-12-R feeding fuse block for Brake lights, tail lamps, dome lamp, cigar lighter, and emergency flasher

My theories are:
1. Loose connections at the bulk head connector causing arcing between connectors creating heat and melting. ( I have seen oven wires do this)
2. Over voltage due to bad voltage regulator ( voltage shouldn't melt things, amperage could)

Looking for any thoughts.

 

[Big_John]

There's a lot of current that runs through that connection to the ammeter. It's known to be a problem.

There's a couple solutions listed here: Vintage Chrysler electrical repairs and updates

 

[Polara_500]

That's the terminal that always fails on these bulkhead connectors and a big part of the reason everyone is bypassing the ammeter so they don't have to pass all current through the bulkhead.

Heh, Big John beat me and gave you a link.

 

[HWYCRZR]

Perfect, thanks guys. I can see why there were issues. Now to figure out what direction I want to go to keep it as original looking and functioning as possible. I might go with the pass through on the firewall (as was recommended for fleet vehicles and taxis). I have some time to think it over before reassembly. Now that I know that running the majority of the car's electrical power through the smaller connectors at the bulkhead were the root of the issue I can work around it.

 

[CanCritter]

good info

 

[MYSINBIN]

Perfect, thanks guys. I can see why there were issues. Now to figure out what direction I want to go to keep it as original looking and functioning as possible. I might go with the pass through on the firewall (as was recommended for fleet vehicles and taxis). I have some time to think it over before reassembly. Now that I know that running the majority of the car's electrical power through the smaller connectors at the bulkhead were the root of the issue I can work around it.

I had this same issue with the Silver Custom. It included a small fire at the voltage regulator. I ended up tearing the entire dash apart and fixing/replacing everything suspicious/not original.

While I understand and agree with the ammeter bypass upgrade, the purist in me just can't do it.

The original design is flawed, but if you think about it, these cars can go years or even decades before catastrophic failure. With zero preventative maintenance.

I removed and cleaned every single wire from the bulkhead block and the three connectors in the engine bay. Anything that was borderline was replaced.

Reassembled with some electrical grease and have not had any issues since.

When you get into it, check the ammeter itself for compromises/melting/loose connections.

I had never done any electrical work like that before. It was overwhelming at first, but the more I learned, the easier it got.

One more thing I'll say:

When it comes to electrical work, learn was it right and fix what is wrong. Guessing can turn your car into a charred pile if scrap metal.

Hope the input helps.

John

 

[65Fury440]

If you don't run through the firewall,there is about 4ish feet of wire you can eliminate, going to and from the ammeter, as well as 2 wire penetrations.
See if you can get the wire from the charge terminal from the alternator, to the starter relay, in a way that you are happy, it might be the easiest way.

 

[crackedback]

Simple solution is to run a wire direct from alternator charge stud to starter relay. Bolt the two connectors at ammeter together. I build the wire around set ups in both 6 and 8 gauge wire which is an improvement over the OEM sizing.

If the bulkhead connector is in good shape, leave the OEM wiring in place, no need to splice or re-route anything. If it's burnt, make any necessary repairs to avoid a fire.

 

[HWYCRZR]

Thanks
I found a new bulk head and connectors. I cleaned up the wires and connectors and re - wired to the new bulk head. Connections are now clean and tite. I really want to keep my ammeter in play. Since using a larger connector through the bulkhead is not feasible, as A fail safe, My other option would be to run a couple of parallel circuits through the empty slots in the bulkhead and wiper connector (there is an empty row). This would give two paths to get power through the small bulkhead connectors. My thoughts are that power takes the path of least resistance. If one of the connectors starts heating up the resistance will increase enough to send the power through the other parallel connection.
At least that is my theory.

 

[Big_John]

Thanks
I found a new bulk head and connectors. I cleaned up the wires and connectors and re - wired to the new bulk head. Connections are now clean and tite. I really want to keep my ammeter in play. Since using a larger connector through the bulkhead is not feasible, as A fail safe, My other option would be to run a couple of parallel circuits through the empty slots in the bulkhead and wiper connector (there is an empty row). This would give two paths to get power through the small bulkhead connectors. My thoughts are that power takes the path of least resistance. If one of the connectors starts heating up the resistance will increase enough to send the power through the other parallel connection.
At least that is my theory.

That's a very good way to do it. It will decrease resistance in the connection.

As far as taking the path of least resistance, that's not really how it works. Think of a circuit with two 10 ohm resistors in parallel. You do the math and it ends up with 5 ohms total resistance for the circuit.

So, two wire and two connectors will split the current rather than all the current going the path of least resistance.

BTW, the math is: total resistance = (r1*r2) / (r1+r2).

FWIW, I've run a #10 wire (with a fusable link) from my alternator to the starter relay as suggested in the article. My car has some added electrical stuff and I felt it would be prudent to do that mod. The ammeter still works, but does not show as much "charge" or "discharge" because the amount of current across it has been reduced. People incorrectly call it a "bypass" when you aren't bypassing anything. You are adding a parallel circuit, reducing the amount of current through the bulkhead and the ammeter.

I also run a voltmeter and that tells me more about the condition of the charging system than the ammeter ever will.

 

[HWYCRZR]

Thanks Big John for at least confirming most of my theory.
It has been a number of years since college when I had to do electrical circuit math. I forgot that all things being equal it would evenly split the load in a parallel circuit.

 

[James Romano]

Another great thread all about this issue and how to address it by Nacho.

Some considerations about the charging and wiring upgrade and your worries about

 

[Big_John]

This is a pretty good thread showing exactly WHAT the problems are and WHY the "bypass" is done.

It's not the ammeter as some seem to think, it's the connections in the bulkhead connector and in the later cars, the power connection under the steering column.

 

[Ross Wooldridge]

I just finished doing the bulkhead bypass on my 66 T&C. I kept the amp gauge wired into the loop though.

Even though some 15 years ago I had cleaned and checked everything down there and packed it all with dielectric grease, it was time to do it properly, as this past fall just before winter nap time I was getting the old "burning wiring" smell, so I knew that was a call for help from the car.

I was a bit overwhelmed about diving in, but I figured I had to. And it wasn't so bad after all...

After peeling the 3 multi pin connector clips off the main bulkhead block, one at a time I removed each individual wire terminal from both the bulkhead and the three clips and cleaned them up with emery cloth (I replaced a few too), and made all of them happy again.

As well, I eliminated the two 10 ga wires going to the amp gauge from running through the bulkhead - and instead ran them as unbroken 10 ga wires through a firewall grommet. I added a multi terminal junction box (NOT a common strip bus bar), and terminated each of the two wires at their own junction block, and then added a fusible link to each one by running the fusible link to another terminal, and then the original wires continued from there to their destinations - the black one runs to the alternator, and the red one to the battery stud on the starter relay, through the original fusible link.

So I'm pretty well covered in the case of any issues, AND I keep my amp gauge function which I like. I also wire brushed all the starter relay studs, and replaced quite a few suspect connectors underhood, and in the process, I figured out how to use my dad's packard terminal crimper - makes them look just like factory! But now I need to buy more 12/14 ga packard male terminals!!

Working methodically it took me about a week, an hour or two every day.

So far so good, and in the short test drives not more burning wire smell, signals and lights are bright and happy, gauges and dash lights are brighter, and I feel more confident over all.

 

[James Romano]

As much as it's almost sacrilegious to some to disturb and even replace the components of a classic car, I firmly believe if you do it right and take your time, you're only prolonging the life of the car.

I actually took my Amp meter out and replaced it with a voltmeter... but you will never tell from looking at it other than when the car is off, it's pointed at discharge. I did this because Amp meters don't really tell you much other than the load is high or low.

My next major project is replacing the glass fuse box with a blade fuse box. Somewhere along the life of my car, a few wires were added in very poorly... and the box is showing it's age anyway.

 

[cbarge]

I just finished doing the bulkhead bypass on my 66 T&C. I kept the amp gauge wired into the loop though.

Even though some 15 years ago I had cleaned and checked everything down there and packed it all with dielectric grease, it was time to do it properly, as this past fall just before winter nap time I was getting the old "burning wiring" smell, so I knew that was a call for help from the car.

I was a bit overwhelmed about diving in, but I figured I had to. And it wasn't so bad after all...

After peeling the 3 multi pin connector clips off the main bulkhead block, one at a time I removed each individual wire terminal from both the bulkhead and the three clips and cleaned them up with emery cloth (I replaced a few too), and made all of them happy again.

As well, I eliminated the two 10 ga wires going to the amp gauge from running through the bulkhead - and instead ran them as unbroken 10 ga wires through a firewall grommet. I added a multi terminal junction box (NOT a common strip bus bar), and terminated each of the two wires at their own junction block, and then added a fusible link to each one by running the fusible link to another terminal, and then the original wires continued from there to their destinations - the black one runs to the alternator, and the red one to the battery stud on the starter relay, through the original fusible link.

So I'm pretty well covered in the case of any issues, AND I keep my amp gauge function which I like. I also wire brushed all the starter relay studs, and replaced quite a few suspect connectors underhood, and in the process, I figured out how to use my dad's packard terminal crimper - makes them look just like factory! But now I need to buy more 12/14 ga packard male terminals!!

Working methodically it took me about a week, an hour or two every day.

So far so good, and in the short test drives not more burning wire smell, signals and lights are bright and happy, gauges and dash lights are brighter, and I feel more confident over all.

Looks good Ross!!
Good for another 300,000!!

 

[Rosco]

Hey Ross,
Couple questions:
-what size alternator are you using?
-did you leave the stock wiring to the ammeter and just eliminate the connectors at the bulkhead and run to the new junction block? (you mentioned 10awg- I thought originally you would have 12awg on the dash side. At least my '68 does)
-you added a fusible link between the alternator and terminal block and are using the original fl from the term. block to the battery? Total of (2) fusible links?

Alright, that's more than a couple.. But, curious, after doing this modification did you determine that the burnt wire smell was coming from where the charging wire passed through the bulkhead connector or do you think you had other sketchy connections?

I'm thinking of doing exactly this- eliminating where the ch. circuit passes through the firewall and using a terminal block.

Nicely done!!

 

[Ross Wooldridge]

Hey Ross,
Couple questions:
-what size alternator are you using?
-did you leave the stock wiring to the ammeter and just eliminate the connectors at the bulkhead and run to the new junction block? (you mentioned 10awg- I thought originally you would have 12awg on the dash side. At least my '68 does)
-you added a fusible link between the alternator and terminal block and are using the original fl from the term. block to the battery? Total of (2) fusible links?

Alright, that's more than a couple.. But, curious, after doing this modification did you determine that the burnt wire smell was coming from where the charging wire passed through the bulkhead connector or do you think you had other sketchy connections?

I'm thinking of doing exactly this- eliminating where the ch. circuit passes through the firewall and using a terminal block.

Nicely done!!

Hey @Rosco thanks for your kind words.

Factory 1 wire roundback alternator - good for 60 amps.

The red and black wires from the amp gauge in the dash were starting to burn at their spade connectors at the bulkhead, so I removed them from the bulkhead. I snipped off their connectors and used two 10 ga butt connectors, crimped and soldered and covered with two layers of heat shrink and then a layer of self sealing rubber insulating wrap (Gardner Bender brand). I did upsize the 12 ga black wire to 10 ga in that union.

I ran them both into the engine bay through an existing grommet, and over to the fender. Originally the red wire would have met with the fusible link at the bulkhead then to the starter relay, so instead, I retained that fusible link coming from the starter relay, and just snipped off the fusible link's spade terminal and joined it to the red wire from the amp gauge at the new terminal block with new ring terminals and heat shrink.

IMPORTANT: the new terminal block must not be a common buss bar - each connection needs to be a separate individual terminal from all the others.

The black wire that goes to the alternator from the bulkhead I did this way - the segment of wire I used when I joined them under the dash I had robbed from another junk harness, and it had it's own factory encased ring terminal, so it went straight to the new terminal block. I made a new 12 ga fusible link from new bulk fusible wire (using ring terminals and heat shrink), and ran that as a loop from the black wire's terminal to another terminal on the block, and then the original wire to the alternator continues from there.

Two fusible links in total, one new, one original. Amp gauge and function retained.

It was totally evident that the red wire was what was burning and stinking at the bulkhead. It was a fire waiting to happen eventually.

I replaced a number of other terminals (both male and female) during the rather forensic examination of all the terminals individually at all connections - bulkhead and charging circuit, wipers, etc. (remove, emery cloth or replace, reinsert), and feel a lot better about the overall system's safety. The new fusible link is a safety redundancy, which is never a bad thing.

I replaced the big 6 ga ring terminal for the red battery cable going to the starter relay as well. Real copper, crimped, soldered, heat shrinked.

I even peeled apart my starter relay and emery clothed the points in there, and wire brushed all the stud terminals.

There you have it!

 

[Rosco]

Wow! thank you for the comprehensive reply!
And, thanks for posting this to the forum for guys like me to see how others are dealing w/ the bulkhead weakpoint.

I especially appreciate keeping the original ammeter in use. I love all the old gauges and the fact that they offer something that back in the day was adequate for the general public so, I really like keeping the original gauge in use.

Sounds like you were a hair shy of a whole new harness!! I have a terminal block (not- buss bar) that I intend to use for the same reason but was going to leave the fusible link at 16 awg. Although your idea of adding an additional one sounds great I'm not sure what size would be the best fit.

I don't know and can't understand why they would have two different size wires in the same circuit from point A (alternator) to point B (battery) 12awg, 10 awg? That's how it is in my '68 and seems like most others that I've read about are wired the same (12awg to 10 awg).

That being said, the original fusible link was sized at 16 awg (following the 4 gauge sizes smaller for the circuit it's protecting rule) I guess to protect the 12awg part of the circuit (the wire starting at the alt. to ammeter to b.c.) ?

My understanding is you would want the FL to be 4 sizes smaller than the wire you're protecting-from the alternator to your terminal block? You said you added a 12 awg fusible link- is this right? Or link size not critical?

Maybe others with better understanding of fusible links could weigh in?

 

[Ross Wooldridge]

It is my understanding it's 2 sizes lower not 4, but I'm nof sure. 10 ga gets a 12 ga fusible link, so that's what I did...