2001 Yukon Headlights will not turn off

[dcragsdale]

The other night when I shut off the the Yukon the headlights stayed on. I had to unplug the headlight relay in the fuse block under the hood to shut them off. I replace the headlight relay but it did not rectify the issue. Only the headlights stay on (in either high and low beam), I went through the sequence to over-ride the automatic headlight mode, the rest of the lights went off but the headlights stayed on. I don't have a wiring schematic so locating another relay etc... is next to impossible. Any ideas would be greatly appreciated.

 

[Sepiroth]

I know we had a Ford Police Interceptor with an issue like this. It turned out being one of the headlight pig-tails shorted in a way that left power to the bulbs.

 

[Grebbler]

If the relay is activating as soon as you plug it in then it's still getting coil voltage from the headlamp switch, Ambient Light Sensor (darkness detector) or the wire leading from these to the relay. You can find out which by disconnecting the headlamp switch. If the lights go out then the switch is at fault.

If the relay is NOT clicking ON then it's more in line with Sepiroths' suggestion above.

The relay you found should be the only one. The brights are controlled on the ground side via the column switch.

There should be 3 headlight fuses. One is a 10A TBC (Body Control Module) fuse located under the hood at position #60(?) that powers the headlamp switch and the darkness sensor). Pulling that should tell you that the trouble points to the dash. The other two fuses are for the right and lefthand headlight harnesses themselves.

If disconnecting the TBC fuse or the headlamp switch don't kill the lights then you have short to +12V at the underhood fusebox or the harness leading back to the dash.

Good luck!

Ed

 

[dcragsdale]

Great info.... One more thing I forgot to mention.... the DRL's no longer function (bulbs are good and I swap out the relay) Here's what happened after removing the TBC fuse, the relay released and the headlights shut off. After replacing the fuse I removed the headlamp switch but unfortunately that appears not to be the point of failure or short. The ambient sensor is working normally. The strange thing is when I shut off the ignition the running lights and dash lights go off, just the head lights stay on. If I do a manual over-ride, then everything will shut off accept the headlights. It looks like I'm going to have to go to the dealer to have the service codes checked. At this point I'm leaning toward either a loose ground or the Hi-Lo beam switch etc.. is malfunctioning. Any other ideas????

 

[Grebbler]

It could be stuck on AUTO which would point to the Body Control Module. This would also explain the DRL's not working as the BCM controls them, also.:cuss:

As a dealer would have the mongo scanner to read it - that appears to be only sure option.

I kinda miss the days of rolling tin foil around fuses to see what smokes to pinpoint problems. This computerized stuff makes my head hurt. :ack:

I feel for ya, man. Good luck.

Ed

 

[dcragsdale]

Ditto..... on the tin foil.... it could be worse, like Lucas ("Prince of darkness") electrical. Thanks for all the great info and insights... Now, if I only had that scanner.... I'll post my
results after I get bent over at the dealership.

 

[dcragsdale]

As thought.... all issues were caused by a faulty BCM. Thanks for the diagnoses help.