The Stovebolt Site Forums The Shop Area The Electrical Bay Flashing lights

My '70 C10 has developed a lighting problem. This involves all lights; headlights, tail lights, dash lights, etc. The lights are continually dimming and brightening. The charging gauge is continually changing from about mid point to around 3/4 or less. I have checked all grounds by disconnecting, cleaning and connecting again. The alt belt is tensioned ok.

What is causing this? Is the altenator bad?

This is driving me nuts and I know drivers in front of me are wondering what is going on. I feel like I am driving a giant strobe light.

This sounds like a main power wire that has a poor connection. If all the lights are powered through the main headlight swith, which I think they are, then I would start there first. Maybe the switch itself is going bad. With the truck off, turn on your lights and watch to see if they dim, try wiggling the shaft of the switch to get them to flicker. Hopefully it is just a loose connection.

Rcimp, I will check out the switch and see what happens.
I have been told that the truck should have a ground strap from the engine block to the body. I just went out and looked and I did not find one. The negative battery cable grounds to the engine block but no strap from block to body. Could this be the problem?

Just went out and turned on the lights, reached under dash and wiggled the wires connected to he switch. The lights did not change so I guess that is ok.

Do your battery posts need to be cleaned?

Battery posts are clean, no problem there.

Improper grounding will always be an issue. If you know there is supposed to be a ground strap from cab to engine and there is not one then add one. Maybe there is one and you just can't see it, (maybe under the cab?). The lights are grounded to to the body, but if the body is not grounded to the engine then the only grounding will be between the cab and fram via the mounting bolts, and they are probably corroded. I would go to your local auto parts and buy a ground strap and install it. It certainly won't hurt.

Does it only happen when you are driving? Or does it occur while the truck is parked, engine running with the lights on?

While it may not be the problem, this is a classic alternator/regulator symptom. If nothing else pans out, you may want to take the alternator (some have built in regulators) to a parts store that checks them.

It also happens while parked with the engine running and lights on. I installed another ground from engine block to the body and that did no good. As soon as I get a chance I am going to have the alternator checked out to see if that is the problem.

In that case, I agree with what Donsz sez.