Mechanics

HEADLIGHTS

1995 GMC Van

Electrical problem
1995 GMC Van V8 Two Wheel Drive Automatic 200000 miles

Headlights recently started flashing like a police car. Going from high beam to low and on/off. Seams to be getting worse. What module could be causing this?
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95vandura
February 12, 2010.



Does this still happen if you manually turn on the lights?

Buddycraigg
Feb 13, 2010.
It stops for a while but starts again.

Tiny
95vandura
Feb 15, 2010.
I've had a chance to look at your schematics and I have a few questions.

Do you have 4 headlight bulbs (2 low and 2 high)
or
do you have 2 bulbs that have the low and high built in to them.

Is the problem on both sides of the van.

Is the light really changing from the high bulb to the low bulb or is it the same bulb but is getting brighter and dimmer?

Buddycraigg
Feb 15, 2010.
I have 4 headlight bulbs (Two high, Two low). It appears to be only the low beams which alternate on and off opposite of each other.

Tiny
95vandura
Feb 22, 2010.
What you are describing does not appear to be possible with a stock headlight setup.

Do you have Daytime running lights?

Buddycraigg
Feb 22, 2010.
No, just the standard parking lights and headlights that you have to manually turn on.

Tiny
95vandura
Feb 23, 2010.
Then I have no explanation.

A single power wire comes out of the dimmer switch and then branches off to the left and the right.

There isn't anywhere for the power to be swapped back and forth.

Unless you have owned the van since it was new, I'm speculating that someone (possibly a highway construction worker) may have installed a flasher system.

I only have 2 suggestions for you.
1 with the engine off, and the lights on, watch for the lights to start flashing and listen for any clicking relays.
Also unplug one of the lights and see if the other side continues to go on and off.

2 start physically tracking the power wire with a test light.

Buddycraigg
Feb 23, 2010.