Ignition Problem with 73 Road Runner

[luther]

I replaced the ignition switch because the engine (318) wouldn't shut down when the ig sw was turned off. But that didn't cure the problem. Even with the new sw installed, the coil is still getting 12 volts when the sw is turned off. I got a wiring diag fm mymopar.com & traced out the ignition circuit, but was unable to find the problem. I tried disconnecting components shown on the wiring diagram that were connected to the coil, but that didn't help. For example, I unplugged the voltage regulator, the ignition module, something called "control unit", and the ignition resistor. I did find out the source of the problem is on the other side of the ignition resistor feeding the coil. When that side of the ig resistor (dark blue wire) is unplugged, the voltage is not applied to the coil. So the constant 12 volts is being fed thru the resistor to the coil. I couldn't find a short in the wiring that would be causing that. Any ideas what might be the problem?
Thx, Luther

 

[70rr-brian]

The brown wire on the same side of the ignition resistor runs to the bulkhead connector. Have you pulled the bulkhead connector? Those are notorious for bad connections. But perhaps you have some sort of crack or whatever in the bulkhead causing wires to touch that shouldn't? Start there.

 

[luther]

Thanks Brian. Does the entire bulkhead come out as a unit, or can you pull individual wires?
--Luther

 

[70rr-brian]

On the firewall under the hood the bulkhead should be pretty obvious to spot....its where all the wires converge on the firewall. You unclip the individual harness of wires (usually 2 rows in a single harness) from either side to lossen them and just wiggle the harness out as a unit. There are usually 3 harnesses stacked one on top of the other. All three will need to be remove seperately. Normally you should check for corrosion and clean with an electronic contact spray clear...but in this case....and again, just a first shot at your problem...I would be inspecting the wires as they run into the bulkhead before removing them to see if there are any signs of cracked or melted wired touching each other. If nothing obvious then remove and look on the inside of the harnesses.

 

[luther]

You were right on, Brian! The bulkhead unit came apart, taking the bundled connectors out on the engine side. But the problem is on the inside. There are 3 wires with insulation burned off! The bulkhead also has burned contacts in it. It looks like I could just replace the bulkhead and splice good wires in to replace the bad spots. I'd rather do that than replace the entire harness! Do you know if that bulkhead is available by itself? The connectors on the engine side look OK, with some clean-up done on 2 contacts.
Thx, Luther

 

[70rr-brian]

Did you verify by seperating those wires and taping them that that fixed your problem? If so, great! Obviously those will need to be fixed but just make sure that is what the problem was if you haven't already.

To be honest...I have no idea where to get a full "stock" replacement one at. I suspect you might have to get a used one if you want to stay stock. Otherwise an aftermarket setup I am sure you can find. I will let someone else chime in on that. I have never honestly looked. Sorry.

 

[luther]

OK, I'm not finding a new bulkhead so far. I have a buddy with junk yard connections. I'll see where that leads.
Thx, Luther

 

[roadrunnerman]

there is a company that sells complete wiring harnesses but can't remember the name, someboby else might,but you definetly need to fix the bulkhead as i had a 74 rr and was going home from work one night and saw a glow down by my feet.The bulkhead had caught fire,luckily i put it out and was able to make it the rest of the way home but had to replace bulkhead and wiring harness under the dash.

 

[luther]

I never found a replacement bulkhead. But I replaced 2 wires that were fried--red and black coming from the ignition switch. I ran them thru a hole with a grommet in the firewall, bypassing the bulkhead. Now the engine can be shut down (no more constant 12 volts on the coil). But now I'm troubleshooting why the damn running lights stay on! Probably something to do with those fried wires. In the mean time, I have to take off the + batt. cable to keep it from running down.
--Luther

 

[70rr-brian]

I never found a replacement bulkhead. But I replaced 2 wires that were fried--red and black coming from the ignition switch. I ran them thru a hole with a grommet in the firewall, bypassing the bulkhead. Now the engine can be shut down (no more constant 12 volts on the coil). But now I'm troubleshooting why the damn running lights stay on! Probably something to do with those fried wires. In the mean time, I have to take off the + batt. cable to keep it from running down.
--Luther

You aren't alone with your wiring issues. I have never seen an old mopar that hasn't been completely restrung with decent wiring. Keep after it...you will eventually get it.

 

[roadrunnerman]

check your wires from the headlight switch thru the firewall.They might have gotten hot when the other wires melted and created an open circuit.

 

[luther]

UPDATE:
Cured constant running light problem by replacing the voltage regulator (don't know know why that did it); but checking the voltage showed the alternator putting out 17 volts and even higher with the battery disconnected. With the new regulator in, voltage topped off at a little over 13V (where it should be). But now there is something still getting battery power with the ignition switch off, so need to find that gremlin! Suspect a short somewhere in the wiring under the dash--on goes the fun!
--Luther