Coil getting constant power with key off

[NWCharger68]

Just bought a '68 Charger a few months ago and while driving last weekend I noticed that when I accelerated the gauges and radio would go dead and the ammeter would peg high. Pulled over to inspect and found the car wouldn't turn off. Made it home. Killed it by pulling the coil wire. Started looking into it last night. I have constant power on the blue wire at the key (key switch removed) as well as the brown. Brown would lose power if the ballast resistor is disconnected but blue is still live. Pulled bulkhead connector apart, looks decent, no melting. Can't figure how blue wire at key and bulkhead are getting power. Possible bridging at the plug for the key? Stumped.

 

[nm9stheham]

Either that, or there is something wrong at the voltage regulator and alternator.

The blue wire to the ballast resistor need to be investiaged. It also feed juice to the VR (voltage regulator). Quesiotn: Does your alternator have 1 or 2 small field wires in the back (in addition to the large alternator output wire)? Originally, it should have 1, but someone may have changed to later 2 wire field and mucked up the wiring. Some pix would be hlepful.

BTW, the brown is being fed power via the blue; I would not focus on that.

 

[NWCharger68]

I took a pic of the alternator. I have one wire from it but it also looks like it has one not being used. With the alternator, voltage regulator and ballast disconnected I still have a live blue wire. One thing has struck me also. Although there is a ground going from the battery neg to the block, should the engine be strapped to the body/frame as well? I'll mock up a ground strap tonight to test that until I can source one. My gut tells me that power is jumping over to blue inside the connector to the ignition switch.

 

[NWCharger68]

Add'l ground strap to body didn't change anything. About to start cutting the harness apart. This has to be a simple fix and I'm going to find it one way or another.

 

[68 Sport Satellite]

Don't know if it can be this simple, but this happened to me before. I replaced my starter and when I hooked it up I accidentally hooked up the wires to the starter backwards. As soon as I swapped them left to right, it worked and shut off correctly. Maybe the guy you bought it from replaced the starter or something else???

 

[NWCharger68]

Looking at the alternator closer and doing some research, it appears I have the newer "square back" alternator. Articles talk about wiring to an electronic regulator. Mine is wired to a mechanical. Re: the starter, this ran great for two months then something happened. One other clue is when testing the field wire connector from the alternator, when disconnected, it had 12 volts on it. I may have a situation where I have the part that failed and also parts that were damaged from the short and/or overcharging. Getting erratic ohm readings on the ballast resistor. Getting a new one tomorrow.

 

[NWCharger68]

Still on the hunt. Pulled the Red power lead from the ignition and the blue wire is still live. Going to have to unwrap the harness and follow the wires until I find the source.

 

[nm9stheham]

You can run the newer alternator from the older mechnical regulator; if you look closely at the other filed terminal on the back of the alternator (the terminal without the regulator wire to it), you should find it grounded.

You should also check the power wire to the regulator; it will likley be at 12v as this is connected to 12v in parallel with the ballast and ingition circuit. Having 12v to the older mechanical VR all the time would explain why you see 12v on the wire from the VR to the field. The VR is looking to make the alternator put out around 14v by pushing current through the field through that wire; with the alternator not turning, it can't so the VR keeps trying to push current to the field. So the VR looks ot be doing its job, but should not have 12v to it on the blue wire with the key in OFF.

If you don't have it already, go here for your car's wiring diagram; it has wires colors and such on it. www.mymopar.com

 

[NWCharger68]

That makes sense on the 12v on the field wire. Just mystified with my blue wire at the ignition being live. It can't be a short or I think I would be blowing a fuse or melting a wire. It must be bridging somewhere but I know it's not at the bulkhead or ignition switch which are the only areas where connections could be compromised. I think this hunt is about to get ugly. I have the wiring diagram and have enlarged it to follow the circuits. I think it's mocking me

 

[nm9stheham]

Well, the insulation could be melted or otherwise compromised somewhere and the blue wire shorted to a 12V wire somewhere. It is just a matter of rooting it out. Pull the connector off of the ignition switch and see if it is still there; that will tell you if it is the switch or the wiring. Also check the connectors very carefully to make sure there are not a few strands of wire shorting between connections.

 

[NWCharger68]

FOUND IT! Unwound the wiring harness from the brake warning light to the bulkhead connector. An inch before the bulkhead, the Ign 1 blue wire (port N) was melted to the black wire next to it in P which is the black return line from the ammeter. That wire has the potential to carry a big load and obviously got warm enough to melt together. Thankfully it didn't melt onto a ground. Seriously considering bypassing he ammeter and putting an inline fuse in. I know it has a fusible link but they don't break the current as fast as I would like if things go bad. Just glad to be moving on from the troubleshooting stage. Thanks everyone.

 

[nm9stheham]

Good deal; glad it shorted in a benign fashion! In the meantime, take the high current black wire out of the bulkhead connector (and the one from the alternator too) and clean it and apply some dielectric grease. To reduce contact resistance even more, there is silver loaded dielectric grease available. Look at the ammeter lugs too for signs of heat.

BTW, fuses are thermal devices just like fusible links, and so will need an overcurrent for a length of time to blow. A typical fuse might take 200-300% of rated current for a few minutes to finally blow. (Feel free to look up a fuse specs and check overload vs blow times....) So don't think it will work better for partial shorts. The alternative is to lower the fuse rating to make it blow faster, but then it will blow easier and you will likley have nuisance blows.

 

[Adam12]

Just bought a '68 Charger a few months ago and while driving last weekend I noticed that when I accelerated the gauges and radio would go dead and the ammeter would peg high. Pulled over to inspect and found the car wouldn't turn off. Made it home. Killed it by pulling the coil wire. Started looking into it last night. I have constant power on the blue wire at the key (key switch removed) as well as the brown. Brown would lose power if the ballast resistor is disconnected but blue is still live. Pulled bulkhead connector apart, looks decent, no melting. Can't figure how blue wire at key and bulkhead are getting power. Possible bridging at the plug for the key? Stumped.

My 1967 GTX would not turn off the other day. 12v on blue wire to coil with key off. Also 12v at ignition switch Brn wire with key off. I am out of ideas

 

[QuickBpBp]

This has to be one of the oldest posts to ever be resurrected as it is from 9 years ago. That being said Good luck finding your wiring issue!

 

[RemCharger]

My 1967 GTX would not turn off the other day. 12v on blue wire to coil with key off. Also 12v at ignition switch Brn wire with key off. I am out of ideas

Read post # 11.