The Stovebolt Site Forums The Shop Area The Electrical Bay Weird Wiring Issue

66 Chevy C10.

Headlight switch in off position = Brake lights and turn signals work great.

Headlights switch on position = Headlights work. Tail lights on but turn signals or brake lights dont work. Tali lights very bright as if brake being applied but not.

bad ground at the taillights

I concur (I always wanted to say that) with 64fleetside. Bad ground. Check it at the place most people check last. The tail light housing.

Take the tail light housings out of the fenders completely. Get some sandpaper and clean all the area where the taillight assembly screws to the fender. Find some star washers to use under the screws. A little dialectric grease at that point of contact won't hurt.

James,

I'm going to disagree with the folks above. It seems if it were a taillight ground issue, that it would only effect the light with the problem...not both. I think it is something else, but I don't have a clue what that would be.

At first I thought 'mashed wires', where the brake light wire and taillight wire were bare and touching each other. If this were the case, when you applied the brakes, the brake AND tail lamps would illuminate! I'll wait for the smart guys to show up on this one!

Stuart

Hey Stuart I'm with you, but I sure hope I'm not the smart guy. I'd like to leave some room for error.

Headlights=on, tail lights but bright, both?

Headlights=off, tail lights and turn signals work, are they dim?

There are three wires to the rear lights, one is tail lights (black) which goes to both, the second and third are turn signal/brake (purple=left, violet=right) one to respective side. If the wiring is correct at the rear lights, and the bulbs are installed correctly, then the problem is either light switch or turn signal wiring. Check the light switch on the right side(?) from the panel they should be dark green, 2 orange to next terminal and then black (this maybe prob wht/blk switched) next see that all the colors on the turn signal harness match. I'm going by a 63 factory manual so there could be some errors. :rolleyes:

Larry

Its a ground problem.

The turn and brake lights are grounding through the tail light circuit. You can test this by removing the lens and carefully grounding the lamp base and then checking to see what the lights do.

Steve,

Wouldn't this lack of ground have to be in BOTH taillight assemblies to affect both sides simultaneously?

Stuart

it generally is both, either thru corrosion in the lamps themselves or no ground strap(bed is bolted thru the wood)from frame to bed.

Brian,

If no ground strap to bed, how the heck do the brake lights function...so this problem is all of a sudden a lack of ground to both taillights only, not the brake lights. I get cornfused trying to draw little cartoons that show how the power is feeding back through odd filaments making them light up when they shouldn't. No cartoon I draw on this post makes both illuminate because of a faulty ground!

Stuart

The first question I would ask is, what, if anything, did you change between its working correctly and now? Or is this an initial setup from an unknown starting point?

The brake lights ground thru the tailight circuit & vice-versa, an 1157 bulb has 2 fliaments but only one ground(the bulb base)don't ask me how I'm no engineer I just know it does.

One possibility is that the brake light and the taillight wires are reversed in both taillight assemblies. The brake and turn lights would appear to work correctly (though they should be less bright than you would expect) and when the headlights are on, the brighter filament would make it difficult to see the brake or turn lights come on.

James,

You had a post on 7/17/07 in this forum dealing with a problem which is almost certainly related to this one. Is there more to this story than meets the eye.

Stuart

Looks like all of you weree riht in ways. I cleand up the ground and the brake lights went off and operated normaly with headlights on. I alos seems o have had one set up the lights wires reversed. Unsure how it worked at all but...bottom line all works well now. Thanks to all.

WOW, multiple gremlins! Time for some Wild Turkey on the roxxxx......glad you triumphed.


Stuart

oops! too late :rolleyes: