Hey all,

I have a 4dr 2000 blazer lt 4x4 I bought it at auction and the daytime running lamps do not come on. The daytime running lamps are required here to pass a mandatory inspection.
Also the front DS highbeam does not come on.
So far I have replaced the multifunction switch & highbeam bulb to no avail. Also I have replaced the DRL relay with no effect.
I checked the park brake, it is off. The headlight switch is set to off. Checked every fuse, no help there.

Any suggestions, frequent wire wear points, stuff like that. This is a nightmare, I already have done a full front end rebuild and now the stupid headlights are failing it ! AAAArgh !

 

Unbolt the underhood fuse panel out and check the bus bars on the under side. Look close for cracks or burnmarks on the bus bars.

 

I after pulling my hair out for hours I found a schematic for the lighting system on blazer forum.
Turns out there is a white wire that goes from the body control module to the light switch. The body control module was not outputting the signal to turn on the lights when the ignition was on. I disconnected the wire at the BCM and connected it to a keyed 12V source. This disabled the flash to pass switch and the parking brake DRL lockout. But the DRL work flawlessly. So I passed inspection.

As for the DS high beam lamp. It gets power from the DRL relay, oddly enough. Someone had installed the wrong relay. It had a 4 pin relay in it. I replaced it with a 5 pin relay (same as fuel pump relay) and now it works.

thanks everybody.

 

There are actually 3 white wires at the BCM that all have to do with lighting. The fuel pump relay only has 4 pins, the DRL relay has 5 pins. Both right side headlamps and the left low beam get power from the headlamp relay. And yes, the left high beam gets power from the DRL relay. The flash to pass feature switches ground through the headlamp grounding relay to control the lamps. There are several things that control the headlamps: autolamp, headlamp switch, flash to pass, DRL's, and the ambient light sensor, so the circuitry has to be more complicated. Let me know if you want to troubleshoot the rest of it. Been there and done that