High beam failure

[Ryan12689]

Hey everyone, I've got a tricky issue with my 2004 P71. I bought this car about 10 days ago and have had the issue since I picked it up, so no history on the problem.
My high beams / brights are possessed. I start my car, flip the switch forward, and they work. Once the car warms up, they automatically go to the low beams, and no amount of flipping back and forth will get the brights to stay on. The only way to keep them on is by holding the switch back.
Is this a bad multi-function switch, a bad headlight switch, or bad wiring under the hood?

[miamibob]

Could be a bad relay in the Lighting Control Module (LCM). Could try "tapping it" to see if that helps, replace the offending relay or the entire module. Sure someone here with personal experience will chime in....Boby

[Ryan12689]

I was thinking an under hood issue because it would only occur after the engine warmed up.

[Ryan12689]

I don't have any shop manuals for this car yet, can anyone point me towards a picture to locate the LCM?

[miamibob]

Should be a rectangular box (black?) to the right of the steering column under the dash. Once you start looking you'll probably find it.

[Ryan12689]

Okay, thanks much. I'll check the relays tomorrow and hopefully that's the problem, I'm assuming it's a somewhat cheap fix?

[miamibob]

Depends upon your electronic skills as the relays are soldered onto a board inside the unit. If you could find a replacement unit that would make for a good test/repair.

[Ryan12689]

So, I've done a lot of research into this. I'm not 100% convinced that it's the LCM. If it is, I'll buy one from a junkyard and help my girlfriend's dad make sure it will work forever, as he's an electrician and I know a little about circuit boards.
My buddy has a 2000 P71. He told me he had his LCM unplugged for months and all his lights would still work, ASIDE from the dash/interior dimmer not functioning properly. Also, all problems
I've seen associated with the failure of an LCM target the low beams mainly, with having no headlights at all being the main symptom.
I'm wondering since I have the dual beam headlights and this used to be a cop car, if maybe some wiring underneath the hood could be overheating? My high beams will only quit after the car is at running temp, doesn't matter what the cabin temperature is at.

[Mainemantom]

I would check the wiring all over the car. When the police equipment is removed, many agencies just cut wires. Their attitude is the car is going to auction, so who cares. Both of my police cars had wiring problems that took months to find and repair. I had many wires cut with sections missing under the dash, under the mat, in the B pillar areas,in the trunk and at the lights. It also could be relays and LCM. I wish you luck.

[sly]

check the fusebox under the hood for a headlight circuit breaker. those are thermally triggered and if it's weak, may act in this way. I don't remember if they ever put those under the hood or if they're in the dash fusebox. I know they moved it off the headlight switch itself sometime during the aero years.

[85crownHPP]

Dunno if this will help, but I got to play with light issues on a civilian-ized whale p71 a few months ago... There is definitely high beam wiring in the trunk, 2 isolated wires should be obviously plugged into each other up in the left of the package shelf, where the goodie modules used to be. I want to say they were both yellow with blue stripe...
Also there is a connection under the hood (this one was on the fender behind the battery) that has two wires that need to be joined into each other. This was one of the car's problems, only one high beam worked, and it was because the 2 wires under the hood got snipped but not joined together. I guess they could be cut and spliced at any point under the hood, but if both work this probably isnt the issue. It looked like the whole front lighting harness was special p71 stuff that all originated from the trunk. Much better than the hack job they did to boxes... lol.

This car also had LCM issues, but it only made the low beams quit.

Dorman makes a cheap plug-and-play bypass/adapter thing for the LCM that costs a lot less than a new LCM.

[Ryan12689]

That helps more than you can know. There is a harness that's hanging loose from my trunk lid but I can't seem to find where it plugs in. I still haven't had a chance to chase down the wiring under the hood.
Any clues on where that free harness would plug in?
Also, where can I find that LCM
bypass?

[Ryan12689]

Thanks so much for all the great info guys. Hope it's warm enough tomorrow to chase down this problem. Need to stop at the auto parts store and get a multi-meter too.

[85crownHPP]

I know O-rileys has it, most other part stores should too.
The wires aren't gonna be in the trunk lid... they used to plug in to a wig-wag box or power source I'd imagine, now they should just be plugged into each other to make the high beams work. Good chance they are tucked away, depending how cleanly the car was de-commissioned. What is left up in the package shelf? The one I was messing with still had the strobe module in it and a couple cool storage boxes, and the slide-out equipment shelf...

[Ryan12689]

It was pretty cleaned out in the trunk. I didn't have a chance to look into it today, too busy and too damn cold. Tomorrow is the day. I'll take pictures of everything I inspect and post them.