Another Baffling Electrical Issue

[Jack O.]

So Im sitting at a stop light about 4 miles from my house in my '69 and it just goes dead. Nothing. No dash warning lights, no lights, etc.

I left the negative battery cable disconnected because the car has a drain and I had removed the quick disconnect as part of my very limited roadside debugging. So before calling it a night once I had the car back in my garage I reconnect the neg cable and now I have interior lights. So then I go to start it and as soon as I turn the key everything goes completely dead again. So I walk away for the night.

Tonight, still dead, that is, I have no interior lights, no headlights, no warning lights when I turn the key on, etc. I check the hot lead on the alternator, the one that comes off the starter solenoid and I have power there. I then go and check power at the horn relay and I have power there also but at some point, the issue goes away again, and everything is back to "normal". Don't know why - all I was doing was using a simple test light to check for 12V at the alternator and horn relay.

I know I had juice at the alternator but can't say for sure about the horn relay since at some point everything came back when I was checking it. Any ideas on where I should be looking or most likely issue if alternator has 12V but nothing else does? Looking at the wiring diagram it appears to me the next major junction is the horn relay.

Thanks,

Jack

[Anthony P.]

Re: Another Baffling Electrical Issue

this same thing happened on my 80.. traced it to the neg cable where it attached to the frame. corroded, passed enough amps to light a test light but that's about all. not saying it is your problem but a place to look! good luck let us know what you find.

[Jim D.]

Re: Another Baffling Electrical Issue

this same thing happened on my 80.. traced it to the neg cable where it attached to the frame. corroded, passed enough amps to light a test light but that's about all. not saying it is your problem but a place to look! good luck let us know what you find.

I had the same problem with a 74. Turned out to be the same issue.

[Jack O.]

Re: Another Baffling Electrical Issue

I'll check that next. I haven't gone under the car yet but definitely need to check that ground. Thanks!

[Jack O.]

Re: Another Baffling Electrical Issue

So my issue is not due to a bad ground from the battery. My car was running and just died. To be sure I tested this by disconnecting the battery, negative and positive, while the car was already running with no ill affect which is what I suspected.

So it would seem that there should only be a few critical areas that would caused this to happen and I'm left with trying to disconnect these critical connections to at least narrow things down. I'm first concentrating on the starter solenoid connections. The harness has seen heat and I definitely see some damage but haven't gotten a real good look yet.

The alternator connections are another area and since it's much easier to get to I may start there. Would a bad alternator cause a car to stop running? Or if the hot wire coming from the starter and going to the alternator was shorted could that cause my issue? I'm grasping at straws here because I don't know enough about how the electrical system works to know where to start looking. Help!

My issue is I can't drive the car until I figure this out because it could die any time. Right now, it's fine making it difficult if not impossible to know I have found and fixed the issue.

Thanks,

Jack

[Joe R.]

Re: Another Baffling Electrical Issue

I'm first concentrating on the starter solenoid connections. The harness has seen heat and I definitely see some damage but haven't gotten a real good look yet.

Hi Jack,

I would recommend concentrating on fixing the portion of the harness that has damage before moving on, even if it's less convenient to access. Often the first step to a successful electrical repair is a good visual inspection. Plus you want the wiring to be safe when you drive the car, right?

Joe

[Jack O.]

Re: Another Baffling Electrical Issue

Thanks for the recommendation Joe. I probably will start there because right now it's the only lead I have. My concern is trying to recreate the issue first so I at least have some hope that I've actually addressed the issue that left me stranded on the side of the road. That's why I'm looking for a way to try to recreate the issue, e.g. if one of those wires does momentarily short out does it cause a running car to just go dead so my thought will be to try and "disconnect" suspected wire while the car is running and see. Of course I'll do it in a safe way. But that's why I'm looking for any suggestions on which wire might cause that type of behaviour.

Jack

[Patrick H.]

Re: Another Baffling Electrical Issue

But that's why I'm looking for any suggestions on which wire might cause that type of behaviour.

Jack

Check the connector that goes through the firewall in front of the driver.
If it was loose or corroded, this exact same thing would happen. It's where I would look since you already checked the battery ground. I'd place it higher on the potential list than starter connections or alternator connections.

Also, there is a ground from the block to the frame on the right hand side. Be sure that one, too, is tight.

Patrick

[Jack O.]

Re: Another Baffling Electrical Issue

So if my car is up and running, which wire or connection, if disconnect or bad, would cause EVERYTHING in the car to lose power? That wouldn't even happen if the alternator went bad unless my battery were bad also would it?

[Patrick H.]

Re: Another Baffling Electrical Issue

So if my car is up and running, which wire or connection, if disconnect or bad, would cause EVERYTHING in the car to lose power? That wouldn't even happen if the alternator went bad unless my battery were bad also would it?

I already gave you the answer.
Short of your battery dying or losing your ground, the firewall connector is the only thing that would do this.

[Jack O.]

Re: Another Baffling Electrical Issue

Sorry, forgot to mention that the firewall connector is tight but of course I know it could still have a questionable connection. I think I understand where you're coming from with that, if it were to lose connectivity, everything I mentioned that died - head lights, inside lights, dash warning lights, etc. - would not work. And I assume it would also cause a running car to stop running also because I would have no ignition perhaps?

Now regarding a dead battery, the Alternator also would have to be bad too since, again, the car was running when everything died. Here's the other interesting clue that I haven't mentioned. Right before I left on this ill-fated trip the battery was dead and I had to jump the car get it started. I let it run a while and then left for a short test drive. It was dark out so I had my headlights on. The car has TI and that also is a draw. If my alternator is bad could it be that the battery simply got drained and boom everything stopped. The only part of this theory I don't understand is that the car remained completely dead even when I was getting a jump on the side of the road - no inside lights no nothing. Which it would seem point me away from this theory and back to something like the firewall connector?

Thanks for the help!

Jack

[Leif A.]

Re: Another Baffling Electrical Issue

Jack,
You said the battery was dead. It's quite possible you have a bad cell in the battery. This will cause a car to stop running as the battery is part of the electrical circuit. Bad cell causes, basically, an open circuit. If it were my car, I would yank out the battery and take it to the local FLAPS and have them put a load test on it. Could save you a lot of angst.

[Jack O.]

Re: Another Baffling Electrical Issue

Battery and alternator checked out good.

Going to do better check on the connector that goes through the firewall in front of the driver as Patrick suggested.

[Mark E.]

Re: Another Baffling Electrical Issue

I second Leif's suggestion.

Eliminate the battery as a possible culprit by replacing it. They're $50 at Walmart. For hobby cars not driven frequently, I favor getting a cheap battery every two years over keeping a more expensive battery longer.

Batteries become capricious and cause unpredictable problems after living a hard life of non-use, discharge, and jump starts.

It may or may not be the root cause of the current problem (pun ), but it sounds like you'll need one soon anyway.

[Jack O.]

Re: Another Baffling Electrical Issue

Yeah, that makes sense. It does seem like more than just a coincidence that the battery was completely dead just before driving the car.

Any thoughts on the accuracy of bench testing the alternator at the local parts store. The guy at the parts store could only tell me that the alternator tested "ok" but couldn't give me the amps output.

Thanks,

Jack