Thread: 1 headlight dimmer than the other?

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On my falcon, I had noticed in the winter that 1 headlight was dimmer than the other ( driver side was dimmer ), so I took the headlight out, looked at it, put it back, all was good... Went out today,trurned the lights on and the problem is back again, bad ground? any suggestions?

I would put a separate ground on the dim headlight and see if that's the proble. Just make up a short wire, tie it into the present ground coming out of the plug and attach it to one of the headlight bucket retaining screws.

Also check the plug for any corrosion.

Thanks, I'll do that

Definitely a ground Matt. Check all the grounds to make sure there isn't a lot of rust.. Clean the area, and the wiring as well.

Definitely a ground Matt. Check all the grounds to make sure there isn't a lot of rust.. Clean the area, and the wiring as well.

Pauls suggestion is a good one. My 66 is doing the same exact thing. Either that or one has it's brights on and the other doesn't which is what I thought it was at first but when I push the brights on the bright one goes a tad bit brighter and opens a LITTLE bit more but hardly can tell. I still haven't fixed the problem and may wait until I get a new wiring harness since the wires are eaten up and sometimes the headlights go out.

It also might not hurt to check the dimmer switch.

I went out tonight took the light out, cleaned all the connections w/ sandpaper and penetrating lube, put it back and still the same, I know the seperate ground goes to the headlight bucket but cannot find it, it gets even dimmer when switched to high beam, I'm pretty shure that indicates a faulty ground. I will check the dimmer switch too.

Originally posted by FMXhellraiser
Pauls suggestion is a good one. My 66 is doing the same exact thing. Either that or one has it's brights on and the other doesn't which is what I thought it was at first but when I push the brights on the bright one goes a tad bit brighter and opens a LITTLE bit more but hardly can tell. I still haven't fixed the problem and may wait until I get a new wiring harness since the wires are eaten up and sometimes the headlights go out.

Do yourself a favor, check the headlights and make shure they cross refrence eachother or are the same part number if the same manufacture. if the dim 1 is a diffrent part number than the bright, theres your problem, simpley a light that is not as bright. and as for the lights going out, may indicate a faulty dimmer.

They are the same. Ground problem I think. The wires on this truck are screwed, really old and brittle. Some of them are not even soldierd together they are just wrapped together. Could be anything but I am pretty sure it's a ground since the connections are rusted all over the place.

I doubt that it is a faulty dimmer switch (could be wrong?) as one wire from the switch operates both low beams lights and the other one wire goes to both high beams.

Did you say you are missing a ground?

Originally posted by FMXhellraiser
They are the same. Ground problem I think. The wires on this truck are screwed, really old and brittle. Some of them are not even soldierd together they are just wrapped together. Could be anything but I am pretty sure it's a ground since the connections are rusted all over the place.

I had the same problem this evening I work the graveyard shift. the ground on my 72 elcomino is the black wire. but the other wires were loose and caused the problem good luck Ed

Ed, isn't any fun is it? I hate messing with wiring. It's not that it's hard it's just that I have no patience with it. I wont be surprised if in the future they have no wires in cars but instead WIRELESS ones! heh

Usually, headlights have three wires (for the high/low beam bulbs). The wire colors are brown, green, and black. The brown wire is the low beam, the green is the high beam and the black is the common, or ground. The black wire typically has a ground lug somewhere near the headlight. Some models run the black wire between the headlights and also have the ground lug at each light.

A dim bulb (car type, that is) and brighter bulb combination can be caused by one of four faults:
1. mis matched bulbs or bulb vendors
2. worn out bulb; a headlight has some finite life, usually less than 1000 hours
3. a bad ground on one side. If the bright side ground is good and the dim side ground is bad, the resistance of the ground is unequal and one bulb gets more voltage (brighter)
4. unequal resistance on the hot side wiring. Most headlight relays have both headlights connected to the same terminal. Sometimes, one wire is partially broken or corroded or has a crimp splice in it creating a high resistance situation that lowers the voltage

You could also install a relay? after many years the wiring gains resistance. Head light manufactures say that the head lights can operate at 12-14 volts, they say they will last longer at close to max. voltage good luck