Headlights not working

[catback23]

My friend has a '92 Buick LaSabre and the headlights weren't working. I checked the bulbs and switch and was able to apply 12 volts to the yellow wire at the LCM (Light Control Module) and get them to come on. So I told him that the LCM was probably bad. He just replaced the LCM with one he got from a junkyard and still the lights aren't working. Personally I'm at wits end and out of ideas other than checking the switch connection at the LCM connector. Has anyone else has this problem and know how to fix it. I did search the forum for this and only found one person with the exact same problems, unfortunately they just went ahead and took it in for repair and all I know was it was a "wiring" problem so that diagnoses doesn't help me much. Any and all help welcomed, if anyone has a wiring diagram of the LCM connectors that would help too.

[tomogchi]

Okay, i had to do this in my regal, and all it costed me was the LCM and 6$ in 10 gauge wire (maybe 3-4 foot), and a fusblock splitter ( i dont know what the exact name of it is)...
Im pretty sure on the back of the lcm, the plug will come right out. and on the plug you should see a set of wires, and I want to say itwas on the left hand side of the plug.... (the side with the large pins coming out of the LCM) and it was an orange wire, and we jsut spliced it, and ran it to the fuse box, with a 30 amp inline fuse, and it worked. And some food for thought. To determine which wire is the power fo the lights, run a wire from the Pos (positive) (on the battery) or from the fusebox. and with a digital multimeter, turn it to the amps selection, and place the pos wire coming form the multimeter to the wire on the fusebox (or batt) and the negative to the wires. With the headlights turned on (and Ignition key in on mode) Poke the orange and Pink wires. I think there was 2 orange, a pink and some other colors. When the current passes through the digital multimeter, it should register some amperage, and the headlights/tail lights/ parking lights, etc. Should turn on. Then just cut the wire, and strip both ends of the plastic, and add the 10 gauge wire, and solder them together, and if yo uwant to get all spiffy, add shrinkwrap. Or you can just electrical tape it. and hopefully voila! its fixed...
I hope this isnt too confusing for you. If you need more help Lemme know. (youve already figured out which wire was the feed, and to actually fix it would require a new wiring harness, so the 6$ fix is more economical, so i thoguht I'd kill 2 birds with one stone, and tell you how to do it; and fix it)
Bill

[catback23]

I got ya, basically the power feed for the headlights was bad so you tapped it into another power feed. 10 guage I have to say for my case is definitely overkill none of the wires at the LCM comes close to being that thick. The thickest one is the pink wire and it's 16 gauge (guessing) everything else is smaller, thanks for the info though I'll check the power feeds even though I know I checked a red, orange, and pink and all were hot with the key on. I'll post my findings after I take a look in the morning.

[spinne1]

If your LCM is working correctly, then it seems it is either the headlight switch itself, or the wiring before the LCM (to and from headlight switch). The headlight switch sends one of two signals depending on whether you hit the headlight button or the park light button. See if you are getting a spike in voltage on two of the wires going to the LCM (and from the headlight switch) when hitting the headlight and park light switches. If you are getting a jump in volts from either zero to twelve, or twelve to zero (can't remember which way this circuit operates--but it is irrelevant) on two different wires when pushing those buttons, then the headlight switch and the wiring is okay. If not, test the headlight switch (getting the door panel off is a major pain without the right tools, which I don't have). If all tests okay, check adding battery voltage to the various non-powered wires in the LCM harnesses. See what happens and find out which run the head lights, and which the tail lights. After this, hook up the LCM harnesses and retest to see if 1) the voltage drops or raises done in the first test above for the headlight switch are still valid, and 2) retest the same wires coming from the LCM that powered the head and tail lights before to see if they are getting 12 volts when the headlight switch is operated.

If you do all of the above and the LCM is getting the signals it should from the headlight switch, and if the LCM is NOT sending out the right signals to light the head or park lights, then your problem is still the LCM and your junk yard LCM was no good (seems possible).