Electrical Gremlins

[banditti]

I have a '77 C10, bought the truck a couple of months ago and it has been running fine. Yesterday, started it up and it idled for a couple of minutes. Threw it in gear and it is like the electrical died. Wouldn't turn over. Lights, etc. pretty much everything but the gauges dead.

Took the battery out today and took it to AZ, tested good. Ran across the street to Napa, tested good. Threw it back in the truck and it started for a couple of minutes... same thing. DEAD

Hooked my test light to the positive, checked ground to block, firewall, chassis, etc. all good.

Went inside, checked google, came out 10 minutes later. On a whim, tried to start it. It started. It ran. Threw my fluke on the battery, 14volts. alternator lug, 14volts. Drove it in the neighborhood for 30 min, no apparent issue.

Tested both sides of the fusible link at the starter and on the firewall.

Replaced the Neutral Safety Switch, nothing.

What should I be looking at?

Thank you in advance!!!

 

[1987 GMC Jimmy]

I have a '77 C10, bought the truck a couple of months ago and it has been running fine. Yesterday, started it up and it idled for a couple of minutes. Threw it in gear and it is like the electrical died. Wouldn't turn over. Lights, etc. pretty much everything but the gauges dead.

Took the battery out today and took it to AZ, tested good. Ran across the street to Napa, tested good. Threw it back in the truck and it started for a couple of minutes... same thing. DEAD

Hooked my test light to the positive, checked ground to block, firewall, chassis, etc. all good.

Went inside, checked google, came out 10 minutes later. On a whim, tried to start it. It started. It ran. Threw my fluke on the battery, 14volts. alternator lug, 14volts. Drove it in the neighborhood for 30 min, no apparent issue.

Tested both sides of the fusible link at the starter and on the firewall.

Replaced the Neutral Safety Switch, nothing.

What should I be looking at?

Thank you in advance!!!

Is it still doing this, or did some of the original issues stuck around but you can drive it now? I didn't hear anything about fuses. This summer a rat chewed about four of my brand new Delco plug wires, and one of the times I didn't see one that was frayed, it got hot, caught on fire, and somehow I blew two or three fuses. Moral of the story, weird stuff can happen and blow your fuses.

 

[banditti]

Is it still doing this, or did some of the original issues stuck around but you can drive it now? I didn't hear anything about fuses. This summer a rat chewed about four of my brand new Delco plug wires, and one of the times I didn't see one that was frayed, it got hot, caught on fire, and somehow I blew two or three fuses. Moral of the story, weird stuff can happen and blow your fuses.

Unfortunately, still doing it. Fuses seem ok. At least my fluke says so Going to check ignition switch and connector this morn

 

[1987 GMC Jimmy]

Unfortunately, still doing it. Fuses seem ok. At least my fluke says so Going to check ignition switch and connector this morn

How do the little battery posts look? I've had issues like this and replaced them because they were rusted, stripped, and felt wiggly on the battery.

 

[chengny]

What should I be looking at?

Not saying this is your problem, but this same thing happened to me a few years ago.

I had the same symptoms; complete loss of power in the entire system for no apparent reason - which would then resolve itself without any action on my part. No obvious problems like; shaky fusible links, broken/loose cables, etc. Battery would always check as good. Started off as just an occasional nuisance, then it became so frequent it was annoying. Finally, one night it happened at a busy intersection. The cops came. They told me if I didn't move it they would have it towed. I wasn't about to pay $150 for a tow to a city lot. There was a gas station right across the intersection and I asked the cop if he would help me push it over. "No can do". Somehow, I pushed/steered that 3/4 ton truck through the intersection and into the parking lot by myself. But that was it, I had to figure out what was going on.

Carefully trace/inspect the battery positive cable from the battery to the starter. Look for any possible points where it could be grounding to the engine or frame. If you do find a ground fault, it won't be a big one (if it was, your cable would melt) and it most likely will not be in constant contact. A worn out area in the insulation - that allows a short to ground - doesn't just appear one day as a big hole. If a cable is in contact with - but not held tightly against - a metal surface, vibration will eventually cause the insulation to wear. But the area of copper conductor that is exposed starts off as a tiny contact point.

And, because of vibration and looseness of the cable, it might not even always be in contact with the chafing point. So at first, the cable itself appears okay. But when that exposed area of conductor does short to ground, it shunts the power straight back to the battery negative and away from the rest of the system.

A short to ground in the primary power cable will most times cause you to lose the plant. Everything will go dead. But, quite often, you will still be able to read voltage at the firewall JB, fuse block, etc. Then awhile later, after the engine has cooled, the cable shifts and the ground contact is lost. Or maybe you make the cable move when you open/close the hood to investigate - or even slam your door shut in disgust.

 

[89Suburban]

I installed a headlight relay mod and the main power feed came off the junction block. Last few weeks every once in a great while I saw the headlights flicker ( now that it is getting darker so early now.) then all if a sudden they just quit working one night on the way to the boat ramp and i pulled in there with just my markers on and of course there is the PO-PO sitting there.

Anyway to make a long story short I spent a few hours diagnosing the wiring and fuses and was getting really pissed off because I kept getting intermittent power readings and I finally traced it down to the crimped on ring terminal at the junction block. The crimped part actually broke off of the ring but the plastic piece of insulation held it together and hid it. And I furiously started ripping apart other connections and crimps apart before in finally found that one at last. As soon as I carved that insulation off it fell out right in my hand. That was actually a first for me seeing that.

 

[89Suburban]

What should I be looking at?

Not saying this is your problem, but this same thing happened to me a few years ago.

I had the same symptoms; complete loss of power in the entire system for no apparent reason - which would then resolve itself without any action on my part. No obvious problems like; shaky fusible links, broken/loose cables, etc. Battery would always check as good. Started off as just an occasional nuisance, then it became so frequent it was annoying. Finally, one night it happened at a busy intersection. The cops came. They told me if I didn't move it they would have it towed. I wasn't about to pay $150 for a tow to a city lot. There was a gas station right across the intersection and I asked the cop if he would help me push it over. "No can do". Somehow, I pushed/steered that 3/4 ton truck through the intersection and into the parking lot by myself. But that was it, I had to figure out what was going on.

Carefully trace/inspect the battery positive cable from the battery to the starter. Look for any possible points where it could be grounding to the engine or frame. If you do find a ground fault, it won't be a big one (if it was, your cable would melt) and it most likely will not be in constant contact. A worn out area in the insulation - that allows a short to ground - doesn't just appear one day as a big hole. If a cable is in contact with - but not held tightly against - a metal surface, vibration will eventually cause the insulation to wear. But the area of copper conductor that is exposed starts off as a tiny contact point.

And, because of vibration and looseness of the cable, it might not even always be in contact with the chafing point. So at first, the cable itself appears okay. But when that exposed area of conductor does short to ground, it shunts the power straight back to the battery negative and away from the rest of the system.

A short to ground in the primary power cable will most times cause you to lose the plant. Everything will go dead. But, quite often, you will still be able to read voltage at the firewall JB, fuse block, etc. Then awhile later, after the engine has cooled, the cable shifts and the ground contact is lost. Or maybe you make the cable move when you open/close the hood to investigate - or even slam your door shut in disgust.

******* ***** cop. Wish I was there to help you push.

 

[chengny]

Thanks man.