Mechanics

HEADLIGHTS

1997 GMC Suburban

Electrical problem
1997 GMC Suburban V8 Four Wheel Drive Automatic 166000 miles

Headlights won't turn on, (low or high beams) parking lamps and turn signals all work ok. Its a Canadian truck so daytime driving lights are on and are working whenever truck is running. I replaced the headlight switch and checked all fuses inside and outside. Also the low beams are brand new. I have been driving the truck for some time just using the daytiime lights along with the running lights, but I'm stumped as to what it could be. Thank you.
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Bobflipp
February 9, 2009.




Have you checked the under hood relay box to make sure all the relay's were good? In the under hood relay fuse box there is a 50 amp maxi fuse(it is fuse number eight) I need you to check that fuse as if this is bad you will have nothing no power to the switch dimmer or anything else within the lighting. The daytime runners are working because they are on a seperate circuit. Get back to me and we will go from there. 8)

Racefan966
Feb 10, 2009.
I checked both 50 amp maxi fuses, both.3 ohms and have continuity. There are only four relays in the under hood housing A/C, starter, horn and fuel pump. All of those items are working. I went through all the fuses with a VOM recently all tested good.

Tiny
Bobflipp
Feb 10, 2009.
Ok so we need to look at the dimmer switch now as all the fuses are good and GM does not use relay's for the headlights. Looking at the wiring diagram the dimmer carries the load. So you should have a yellow wire and a tan wire at the dimmer switch check to see if they both have power if there is power getting to it then check the green wire as that it what goes to the lights and see if there is power coming out of it. If no power is coming out then replace the combo switch as it is bad. Now if no power is getting to it then we need to check the day time running light module as it send the power there.
Check the daytime running light relay for power at the pink wire. Let me know what you find and we will go from there.

Racefan966
Feb 11, 2009.
I have chased the path on the schematic as well. This dimmer switch is located in the column. Where can I check voltage of the tan and yellow wires? Is the molex easily accesisible. It seems unlikely that the DRL module is bad.

Tiny
Bobflipp
Feb 11, 2009.
I stll need you to check the power going to the DRL Module to make sure there is power there it is a pink wire. Now I also need you to check fuse number 4 and 9 make sure they are good. If you have fog lights do they work?
Your DRL mudule controls the high beam power thru the dimmer which is part of your multi function switch. So the module could be not sending that signal therefore no headlights. Let me know what you find and we will go from there.
AD

Racefan966
Feb 12, 2009.
I will do that. I won't have time to do it until Sunday.
Where are these test points located?

Tiny
Bobflipp
Feb 12, 2009.
OK the DRL is behind the left side of the dash taped to the panel wire harness. Do you have factory fog lights? Do they work if you do?

Racefan966
Feb 14, 2009.

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