My engine wiring harness burned up a couple wires yesterday!

[timk225]

I have a post in the Racing forum, wherein I took my 1973 Duster /6 out for a speed run and made it all the way to 87 mph, followed by the ammeter going to full discharge, a big backfire or loud POP, followed by a brief pause on the side of the road.

This morning the car would not start up. It cranked fine and had gas, but no spark. I researched testing coils and distributor pickups today at work, put the time to good use.

So this evening I started getting into the engine wiring and found what caused the problem. An alternator field wire had finally had enough of its 52 year old insulation, and shorted out a wire along the valve cover hard enough to make about a foot of insulation disappear. I unwrapped the wiring enough to get that wire all pulled out of there, from the alternator to about the #5 spark plug.

As for the distributor pickup, when I test its resistance at the plug, I'm getting 400 ohms, which is in the good range. But then I go to the ECU plug and test it there, I'm getting 8 ohms. So something is still shorted out in there somewhere.

I can bypass the factory wiring and run wires directly from the distributor plug to the ECU plug and see if it runs. I did the same thing back in '10 on my '89 Dodge Turbo Spirit 2.5 when one of the 4 injectors decided to start firing when it shouldn't, causing fuel to drip out the tailpipe and contaminate my new engine oil with gas. I eventually traced it to the #3 injector and used a junkyard injector wiring plug to bypass the factory wiring and run a new wire the the computer plug for that cylinder. It ran fine like that for the remaining 3 years I had that car.

As for my Duster, the most amazing thing to me was that after the wire shorted out, once the engine sat for a couple minutes, I started it and drove it 20 miles, including a stop and restart along the way with not a single problem, then this morning it wouldn't start.

 

[Oldmanmopar]

More than likely you lost the 12 volt start from the ignition but still had the 8 volt run. Until you shut it off.

 

[str12-340]

buy an engine/forward light harness and replace the whole thing

 

[timk225]

buy an engine/forward light harness and replace the whole thing

Yes, I got an M&H wiring harness on order from Year One tonight, the HU2 harness. I had called them a few weeks ago and asked about them. I'll have to extend a few wires to work with a Slant 6, but it will certainly be better than what I have now. I even googled "Year One discount codes" and found one that worked and saved 20% on it!

 

[67Dart273]

..............Or untape the whole thing inspect and replace wire by wire. That is sure one problem with these girls, the "run" circuit, the start (yellow), the VR circuit none of that is fuse protected, and the fuse link is damn poor.

 

[timk225]

In this car, the electrical genius who owned the car before me did all sorts of creative things.

One of his big ideas was that he ran a whole new thicker power wire from the alternators' output post, through the firewall to the ammeter, then back to the starter relay by the battery. So the alternator main wire going through the firewall connector appears to be bypassed. He did include a fusible link in the wire next to the starter relay, and that link is a thin purple wire, so I'm sure it would blow if it had a problem. One of the field wires on the alternator was the wire that got smoked the other day. The field wires were in the original wiring harness.

I'm planning to keep that power wire setup as it is for now, to keep excess power from flowing through the 52 year old firewall connector. Anyone have ideas about this?

When I was at Lowe's yesterday, among other things, I picked up an automotive fire extinguisher to keep in the car.

 

[1969383S]

In this car, the electrical genius who owned the car before me did all sorts of creative things.

One of his big ideas was that he ran a whole new thicker power wire from the alternators' output post, through the firewall to the ammeter, then back to the starter relay by the battery. So the alternator main wire going through the firewall connector appears to be bypassed. He did include a fusible link in the wire next to the starter relay, and that link is a thin purple wire, so I'm sure it would blow if it had a problem. One of the field wires on the alternator was the wire that got smoked the other day. The field wires were in the original wiring harness.

I'm planning to keep that power wire setup as it is for now, to keep excess power from flowing through the 52 year old firewall connector. Anyone have ideas about this?

When I was at Lowe's yesterday, among other things, I picked up an automotive fire extinguisher to keep in the car.

After I lost my 69 Super Bee to an Electrical Fire I just replace everything regardless of how it looks. And yes a fire extinguisher is always within reach! Smart Move!

 

[67Dart273]

In this car, the electrical genius who owned the car before me did all sorts of creative things.

One of his big ideas was that he ran a whole new thicker power wire from the alternators' output post, through the firewall to the ammeter, then back to the starter relay by the battery. So the alternator main wire going through the firewall connector appears to be bypassed. He did include a fusible link in the wire next to the starter relay, and that link is a thin purple wire, so I'm sure it would blow if it had a problem. One of the field wires on the alternator was the wire that got smoked the other day. The field wires were in the original wiring harness.

I'm planning to keep that power wire setup as it is for now, to keep excess power from flowing through the 52 year old firewall connector. Anyone have ideas about this?

When I was at Lowe's yesterday, among other things, I picked up an automotive fire extinguisher to keep in the car.

MAY be fine, depending on how it's wired. The factory did a similar deal on optional 65A alternators, known commonly as "fleet, police, taxi" wiring. They ran larger wires through individual gromments through the firewall, chopped off and taped (I think the red) one of the original ammeter wires. The other issue can be the ammeter itself.

 

[timk225]

I ran 2 jumper wires from the distributor pickup plug to the ECU, and the engine fired right up. But the alternator is not charging. I don't know if a shorted wire damaged one field of the alternator, or a messed up alternator field burned the wire. Either way the alternator needs fixed, but no big deal, as I was going to have it rebuilt anyway for maintenance purposes.

I got in touch with M&H tech today to ask about buying some extra wire for extending some of their HU2 harness plugs for use on the /6. They directed me to their website, where it said that the wire they use is as good as what is in newer vehicles. So I'll save the money and head to the junkyard with a pair of wire cutters and salvage some wire!

 

[67Dart273]

I would do some quick/ dirty testing. Alternator may not be hurt, unless it suffered fire/ flame.

Check continuity of the field. Ohmeter connected to the two field terminals should be a very low reading. With one lead of the meter to the case, either field should show open.

With some alligator jumpers, ground one / either field, and jumper power to the remaining. This should cause the alternator to charge full output, if the output wire is still hooked to the battery. Check for breaker/ fuse/ fuse links, etc

 

[Mattax]

An alternator field wire had finally had enough of its 52 year old insulation, and shorted out a wire along the valve cover hard enough to make about a foot of insulation disappear.

followed by the ammeter going to full discharge,

As for my Duster, the most amazing thing to me was that after the wire shorted out, once the engine sat for a couple minutes, I started it and drove it 20 miles, including a stop and restart along the way with not a single problem, then this morning it wouldn't start.

One of his big ideas was that he ran a whole new thicker power wire from the alternators' output post, through the firewall to the ammeter, then back to the starter relay by the battery. So the alternator main wire going through the firewall connector appears to be bypassed. He did include a fusible link in the wire next to the starter relay, and that link is a thin purple wire, so I'm sure it would blow if it had a problem. One of the field wires on the alternator was the wire that got smoked the other day. The field wires were in the original wiring harness.

A. The fusible link(s) did not melt. If the second pair of wires to the ammeter were done like the factory optional fleet method, then from what we've seen the standard wire to the ammeter was disconnected.
Post up some photos of the wiring. Will be able to tell you pretty quickly if its factory or a modification.
There was also fleet version shown in the FSM for B-bodies that used the standard blue fusible link to protect the 12 gage wiring and a 14 gage link to protect the 8 gage wires.

B. You didn't say what the ammeter was showing as you were driving, but obviously it was discharging becaue that was the only power source to start and run the car for 20 miles. So the battery needs to be recharged.

C. Which field wire shorted? If its the blue one, then the short was before the alternator.

Check the FSM but the ignition run wires are like 16 gage and 18 gage to the field terminal. The fusible will not protect the 18 gage wire at all. Harness tape and good support was the all the protects the wires from getting chafed.

 

[timk225]

A. The fusible link(s) did not melt. If the second pair of wires to the ammeter were done like the factory optional fleet method, then from what we've seen the standard wire to the ammeter was disconnected.
Post up some photos of the wiring. Will be able to tell you pretty quickly if its factory or a modification.
There was also fleet version shown in the FSM for B-bodies that used the standard blue fusible link to protect the 12 gauge wiring and a 14 gauge link to protect the 8 gauge wires.

B. You didn't say what the ammeter was showing as you were driving, but obviously it was discharging because that was the only power source to start and run the car for 20 miles. So the battery needs to be recharged.

C. Which field wire shorted? If its the blue one, then the short was before the alternator.

Check the FSM but the ignition run wires are like 16 gauge and 18 gauge to the field terminal. The fusible will not protect the 18 gauge wire at all. Harness tape and good support was the all the protects the wires from getting chafed.

I'll have to look tonight after I get home. I think the field terminal that had the problem was the one "in the middle" between the main alternator output stud and the other field wire. I have a 1972 Plymouth and 1973 Dodge factory service manual on my computers, I'll be able to follow the wires for the alternator in them.

And it was the original wiring harness. Old, stiff, and likely cracked insulation. I know the ammeter only has these "extra" wires going to and from it, there's not a second pair of wires on the ammeter. I attached them when putting the rebuilt instrument panel in a month or so ago.

 

[Mattax]

I'll have to look tonight after I get home. I think the field terminal that had the problem was the one "in the middle" between the main alternator output stud and the other field wire. I have a 1972 Plymouth and 1973 Dodge factory service manual on my computers, I'll be able to follow the wires for the alternator in them.

And it was the original wiring harness. Old, stiff, and likely cracked insulation. I know the ammeter only has these "extra" wires going to and from it, there's not a second pair of wires on the ammeter. I attached them when putting the rebuilt instrument panel in a month or so ago.

The field terminals on the alternator are interchangeable.
The feed wire can go on either one, although the factory was consistant in terms routing. A mechanic who didn't care or was unaware could switch them and it still works.

Here's my interpretation of the optional '60 amp' alternator wiring for a '73 Dart.
This scheme seems to be the one used on cars with rear defrost grids.
I've been told that the standard alternator wire was removed (or disconnected).
But I don't know that as a fact. Or, it may have been different on cars that did not have rear defrost grids but ordered the option for some other reason.

Regardless, this scheme uses a single 16 gage fusible link.
If the standard alternator output was retained, it doesn't effect anything operationally.

 

[Mattax]

Here's the route current flows through the rotor and regulator.

So its possible the alternator and regulator could be OK.
Since electrons actually flow from negative to positive, I don't know enough to say for sure, but its certainly possible the components are undamaged.

Also we can see the diagram indicates the field wires are 18 gage

 

[timk225]

Update. I went to the car and did some testing yesterday. It still starts up and runs, but it isn't charging the battery. Having seen the diagrams above. I pulled the plug off the voltage regulator and tested for continuity to the field wires at the alternator. The green wire was ok but the blue wire was not. With the engine running, a screwdriver touched to the alternator rear bearing shows no magnetic attraction. I don't know if the blue wire being bad is causing the alternator to not charge, or if the alternator got damaged with the wires shorting out.

Also, at the rear of the engine where the wiring goes around it, I noticed that there extensions about 6 inches long spliced into most (but not all) of the wires heading to the distributor, coil, temp sensor, alternator area. I wonder if this is an original V-8 wiring harness put in to replace the factory /6 harness. The new one I am getting is a V-8 one, and I'll have to modify a few wires as needed.

 

[67Dart273]

Connect everything as normal. Get your meter and turn the key to "run."

Backprobe the blue field wire at the alternator. If you cannot access it, switch the green and blue field wires at the alternator. Does not matter. You should have very close to battery voltage at that point.

Pull the VR connector. You should show battery voltage at both the pins in the connector.

If you know how to measure current with your meter, and if it has say, a 10A or larger current scale, stick one probe to ground and stick the other in the green wire terminal of the VR connector, and still with key in run, and everything else normally connected. This will ground the field and show you the current through the field. The field current test is in the service manuals. Current varies, but at least 3A or so

The VR MUST be grounded. Clean/ scrape paint off around the bolt holes, and get yourself some star lock washers.

This is a simple circuit. The VR blue IGN terminal MUST be at battery potential, and so must be the case. The VR so to speak controls the "amount of ground" on the green. The blue to the field supplies power, and the green controls the current flowing in the field, in order to control charge rate.

 

[timk225]

I did that for testing. I put the key on "run" and put one multimeter lead on the blue field wire of the alternator, and the other on the "center" blue wire plug of the voltage regulator connector. I was getting 7 volts. I also had 7 volts on one side of the dual ballast, and it was getting hot after just a few minutes. The green wire in the "side" of the voltage regulator plug had no volts. Blue field wire to battery positive was also 7 volts.

My guess is that something is still shorted in some way? For the ballast to be getting hot quickly?

The blue wire leading to the alternator is the one that got smoked the worst. I should mention that near the rear of the engine, that wire had a "Y" connection, and the other wire ran up to the exhaust manifold mounted electric choke for the Holley 1920. That wire has a broken tip for a while so I used it to connect to the alternator field, since whatever is in it is coming down the same wire from the voltage regulator.

My multimeter doesn't have a setting for measuring amps.

I also had taken the voltage regulator loose last week and cleaned and reseated all its ground points, there was more than 1, the previous owner was ground-happy and had extra wires going to grounds on different things.

 

[Mattax]

I did that for testing. I put the key on "run" and put one multimeter lead on the blue field wire of the alternator, and the other on the "center" blue wire plug of the voltage regulator connector. I was getting 7 volts. I also had 7 volts on one side of the dual ballast, and it was getting hot after just a few minutes. The green wire in the "side" of the voltage regulator plug had no volts. Blue field wire to battery positive was also 7 volts.

My guess is that something is still shorted in some way? For the ballast to be getting hot quickly?

The blue wire leading to the alternator is the one that got smoked the worst. I should mention that near the rear of the engine, that wire had a "Y" connection, and the other wire ran up to the exhaust manifold mounted electric choke for the Holley 1920. That wire has a broken tip for a while so I used it to connect to the alternator field, since whatever is in it is coming down the same wire from the voltage regulator.

My multimeter doesn't have a setting for measuring amps.

I'd have to reread this a couple times to figure out what youu tested. If current is flowing between two locations, 7 volts shows significant resistance.

the blue wire was not

By which you mean no continuity??

I don't know if the blue wire being bad is causing the alternator to not charge

Go here and read the explanation of how it works.

Identifying Chrysler Alternators (1960-1976)

Roundback and Squareback refer to the style of housing. Roundback through model year 1969. Roundback for model years 1970-71 usually has a slightly different rear housing Squareback Revised Squareback Is most easily differentiated by the thin middle between the housings. Overall these...

www.forabodiesonly.com

Then look at this diagram again.

, I noticed that there extensions about 6 inches long spliced into most (but not all) of the wires heading to the distributor, coil, temp sensor, alternator area. I wonder if this is an original V-8 wiring harness put in to replace the factory /6 harness. The new one I am getting is a V-8 one, and I'll have to modify a few wires as needed.

If you post some pics we might be able to tell you.

 

[timk225]

Here's some new photos. The thick tan / off-white wire I am holding in one photo is the alternator output, it goes to the ammeter, then a red wire of the same thickness goes to the starter relay with a thin fusible link wired in at the relay end.

None of this is my engineering, except the 2 temporary wires (white and red) that go to the ECU from the distributor to get the engine running again.

I had already planned rebuilds for the starter and alternator purely for maintenance purposes, so I pulled them today. The new wiring harness is on the way, so none of this wire will be used again. I'll probably also put the voltage regulator on the firewall next to the brake booster where it belongs, instead of on standoffs on the inner fender as it is now.

What size (amps) alternator is this? It has a dedicated ground terminal which was used and will continue to be used.

 

[Mattax]

What size (amps) alternator is this? It has a dedicated ground terminal which was used and will continue to be used.

Back case looks like a revised squareback.

Where do you see a ground terminal???
There were optional alternators with slightly different wiring, but the regulator looks standard. (I didn['t check the part number.)

 

[Mattax]

Engine Connector CE 37 deleted by a previous mechanic

The thick tan / off-white wire I am holding in one photo is the alternator output, it goes to the ammeter, then a red wire of the same thickness goes to the starter relay with a thin fusible link wired in at the relay end.

The tan looks like a factory high amp alternator output wire.
It goes through a grommet?

The next question is how doe the car get power?
Are there other wires on the ammeter stud?
If so, that's one of the factory heavy duty methods.

 

[Mattax]

1973 HD wiring from the firewall back.

How rare is electric rear defrost?

Not an accurate one. I've had acouple good offers for the switch. But wanna give someone a chance to buy it all complete first before I separate it all out. Depending what shipping ends up being, I’d be interested in the whole setup.

www.forabodiesonly.com

Here's a '74. Might be a slight change in the firewall between 73 and 74 I can't remember.

 

[timk225]

Back case looks like a revised squareback.
View attachment 1716410408
Where do you see a ground terminal???
There were optional alternators with slightly different wiring, but the regulator looks standard. (I didn['t check the part number.)

That small silver nut and bolt at the bottom of the photo, has GRD cast into the housing and it is being used as a ground terminal to the radiator support, with other grounds also attached there. At least, that is how I got the car.

 

[timk225]

Engine Connector CE 37 deleted by a previous mechanic
View attachment 1716410409


The tan looks like a factory high amp alternator output wire.
It goes through a grommet?

The next question is how doe the car get power?
Are there other wires on the ammeter stud?
If so, that's one of the factory heavy duty methods.

The tan alternator power wire goes through the large plastic plug on the firewall, next to where the steering column goes through. There are no other wires on the ammeter. Just the tan going in and a red wire of similar size coming out to the starter relay.

 

[Mattax]

If the side view shows a thin stator frame, then that's a later revised squareback. I'm going to guess that there was some application that used an extra ground. Or, it is possible that an extra ground was added to the original alternator.

If the car came with a Chrysler built 60 amp alternator it would have the standard squareback case.
This is a '73 casting.