Electrical Problem

[TexRiv_63]

I just had a frustrating but educational car electrical problem. Last Friday I started my 66 Dodge wagon up and moved it to the center of the garage to do a little maintenance. Shut it off, did my stuff, then went to start it and take a ride. One click, then no power - complete electrical shutoff to the whole car. OK, checked the battery voltage, it was 12.8. Checked and cleaned the cables, found a loose ground cable that was tightened to the max - Aha! Bought a new parts store cable and installed it, still dead. Had the less-than-year-old battery tested, it was fine and fully charged. Posted to a couple of online forum electrical threads and the horror stories began, mostly about fusible links and the bulkhead connector. No obvious visual clues, tried jumping connections, wiggling wires, etc. with no effect. Pulled wires from starter solenoid and horn relay and cleaned all terminals, no effect, By now I had fiddled into Saturday and gave up pissed. Late Saturday night I saw another forum post talking about jumping the negative terminal - I realized I had been spending all my time on the positive side, ASSUMING the negative was good since I had replaced the cable. Ran out to the garage, pulled the headlight switch and jumped the negative post to another ground - the lights worked!

When I did my A/C conversion I connected the ground cable to the compressor frame and it worked great - until Friday when it stopped working. I switched the cable to an exhaust manifold bolt and the whole problem was fixed, everything worked fine. I have to assume my compressor ground turned bad due to painted and powder coated surfaces, just surprised that it worked initially. Good lesson for me and a reminder of the immutable rules of car electrical systems:

RULE #1: Double check for a good ground, stupid!
RULE #2: See rule number one.

[JACK M]

I know an old guy I know says "90% of all electrical problems are groundless"

Edited February 4, 2020 by JACK M (see edit history)

[FLYER15015]

Don,

That was a good ground choice, since a manifold bolt goes directly into the block.

NOW go underneath and run a good ground cable from the bell housing to the frame / body.

Just for "insurance".

Mike in Colorado

[joe_padavano]

On 2/4/2020 at 12:39 PM, TexRiv_63 said:

I have to assume my compressor ground turned bad due to painted and powder coated surfaces, just surprised that it worked initially.

 

Your problem was likely galvanic corrosion due to the dissimilar metals. The new, clean aluminum compressor housing was a great conductor when new. Unfortunately, the joint between that aluminum housing and the steel bracket eventually built up a layer of aluminum oxide due to the galvanic action of the dissimilar metals. Running the ground cable directly to the iron block is a better choice for several reasons. In addition to taking the aluminum out of the circuit, every bolted joint adds resistance to the circuit. Minimizing those joints reduces voltage drop. Finally, no matter where I run the ground cable, I always use a touch of dielectric grease to minimize the chances of corrosion.

[lostviking]

If it was me, I would not use the exhaust manifold bolt. That gets a bit hot, and will likely melt the insulation. OK, it's just ground, but still. Move it to the block if you can. Just cosmetic of course. You could switch to a grounding strap instead of the insulated cable too.

Edited March 1, 2020 by lostviking (see edit history)

[Bloo]

Heat promotes corrosion. It will work on the exhaust, but would be better somewhere else. The block is also slightly better than the head, but now I am splitting hairs.

[Bloo]

No frame on this car other than a stubby subframe at the front. The body ground does not take any starter load. The strap is a little one that runs from the back of the engine up to the firewall. They hardly ever fail, but it should be checked.

[avgwarhawk]

One bad ground can ruin an entire day.