'71 w/Intermittent Electrical Power Problem
 

I have a '71 K5 Blazer with the original points ignition. Sometimes it acts as though there is an open circuit from the battery somewhere (no headlights, no courtesy lights, won't crank). The battery and its connections are good. I replaced the ignition switch thinking this was the problem. When it is dead I can't revive it, but if I come back another day sometimes it is okay.

What else should I look at? I'm beginning to think it is possessed...

Wes

I have had the same problem on my '72 before. Once, i was driving along after dark, on a moonless night, and the whole truck just died. Motor stopped, no lights worked, nothing electric. I had to feel around and find my flashlight. Turned out that the wire that goes off the + battery cable, the 10ga lead, had fallen out of its connecter. The connecter was the little black box (about 1"x1") that is mounted on the passenger side fender, next to the battery. If you loose a connection there, everything will go dead because all the power in the truck goes through that point. I would check all the connections on that wire, and trace it all the way up to the alternator. Also, check for a bad ground somewhere. Bad grounds have been known to do some pretty weird stuff.

I know you said the bat connections are good but if by chance you are using the after-market replacement cable ends that clamp onto your old cable many times folks don't think to check and clean both ends of that clamp, the bat end and cable end.

Fuse panel
 

I've seen corrosion in a fuse panel cause an intermitant problem with all of the electrical. It also was causing some fuses to blow as well.....?????:flag:

Check and clean all grounds!!!!

I agree with everybody. I've had the same problem as you and it was the terminal end on the passenger fender. I finally just bypassed it and installed a 50 amp fuse sodered in its place. Also having problems now with the fusebox corrosion. Had drivers door off for a couple of months while doing body repair and have been fighting the fuse box ever since. Truck was outside. My shop is my driveway. NO work when it rains.

Sounds like you have a bad ground. I would check the gound wire that attaches to the block. Take it off and check the wire and clean the block where the wire attaches. There should be another wire that comes off the ground terminal of the battery and attaches to the body. I would check that and clean where it attaches. Need to make sure you have a good metal to metal connection. You might have another wire coming off the block and attaches to the frame. I just check my 72 chevy and it looks like I don't have a wire from the block to the frame. Hope this helps.

Thanks everyone! It turned out to be the black terminal box on the passenger fender. I cleaned the connections, greased them, and added an externally toothed lock washer.

Wes S.

Glad you found it.I had one more suggestion to add.I had a car in HS that would take a notion to not crank or anything once in a while.I spent months looking for the problem and replacing parts.I finally found that by using a jumper cable from the battery to the starter it would start.The cable had corroded inside the insulation and would make contact or not sometimes affected by the temp.

Lots of good advice here. I've fought many similar battles a while ago but most of mine involved finding a short that would drain the battery (finally found it in the steering column).

One question: What does the black terminal box on the passenger fender do? It's been so long since I bypassed it that I forgot where it hooked to and what it did.

Thanks,
Mike

Someone can correct me if I'm wrong, but the black terminal box just looks like a convenient way to tie the power lead from the battery into the rest of the truck's harness.

I remember when the wire came off the little box, while i was driving it came off, when it came off the voltage regulator suddenly didnt have any power going to it which caused a big voltage spkie in my electrical system, burned out quite a few lights and ruined my tach. now i learned to use fuses.