1972 Cadillac Headlight Problem

[Coupe Deville]

Hello everyone.

I'm having a problem with the drivers side low beam headlight on my CDV. Last week the headlight went out, I thought it was burned out. I opened the hood and wiggled the connector to no avail thinking it was a bad connection. I closed the hood and the light popped back on. So I drove home, and It was fine for the next few days. Yesterday night the light went out again. But I have discovered that the light comes back on when the high beams are turned on. So that rules out the light being burned out. Could anyone point me in the right direction about this one? Definitely sounds like a wiring issue now.

One good thing, having the fiber-optic light warning system is awesome. Very helpful in this situation. New cars should have them too.

Thanks

-Gavin 

[Scot Minesinger]

It still may be the light bulb - switch driver/passenger to be sure.

Usually this problem is centered around the floor mounted foot activate bright switch, start there for a wiring problem.

[Jeff Rosansky CLC #28373]

The low beam can go out and still have the hi beam work.
Jeff

[Lucas Feininger #15674]

I had a similar problem years ago with a Buick Riviera.

The low beam bulb had two filaments in it. One came one when the low beams were on, both came on (as well as the separate high beam bulb) when the high beams were on.

I would replace the bulb.

[Dan LeBlanc]

When you closed the hood, it may have rattled the filament enough for the two broken/burned ends to touch together allowing the light to operate again for a short time.

Done this a few times with burned out light bulbs in the house when we were out and didn't feel like going to the store to get more.  Usually got me through a day or two until I was passing by a store to pick up more.  Yeah, I know, I'm cheap.

[m-mman]

The sealed beam headlight bulbs used since 1940 all have either two or three metal prongs on the back. To test a bulb connect one to a 12v battery positive and the other to the 12v battery negative. Since its a bulb there is no polarity it either works or not.

On the 4 bulb systems the high beams have three prongs. Low filament, high filament and ground.
In the crudest manner you can connect a 12v battery between two of them and watch one filament glow then switch to the other. It is hard to do it wrong.

Plugs do get dirty. They are almost impossible to get any brush type thing inside to clean. Blow them out is the best I have been able to do.

There are 2/3 slots in the plug (depending on the bulb) One is 12v power the other is a ground.  (or two 12v power in and the third is a ground) The ground wire is small and held to the body with a self tamping bolt that has been known to unscrew slightly and become corroded.

Tracing this ground wire (it is always close to the headlight assembly - one for each side) Unscrewing it then cleaning and polishing the 2-3 ground wires it is holding down and then retightening it is always a simple and worthwhile maintenance activity.

[Scot Minesinger]

was it the headlight?

[Coupe Deville]

Hello Scot,

Been off the site for awhile. You were all correct, it was the headlight. Thank you for all of the great suggestions.

-Gavin