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Thread: Troubleshooting the headlights

  1. #1
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    Default Troubleshooting the headlights

    So, the headlights. A pain in the arse in case of my MGM. After a series of tests, I am quite sure that the situation looks like this at the moment:

    -> the autolamp system works ok, turning on and off the position lights, cluster lighting and low beams whenever necessary;
    -> the switch... probably it works well, too, at least for the positions;
    -> switching on high beams screws everything: if the car is on autolamp, but the headlight switch is set to off position, there is a weird noise coming out of one of the relays under the dash and ALL lights go out; they will come back after a while, but as long as the high beams are on, the situation will persist;

    To ensure I have some lights in any situation, the electrician has made an additional circuit that turns the low beams on as soon as the ignition is on; if this is plugged in, then turning the high beams on results in an intermittent operation: they switch on and off from time to time.

    Any obvious suspects? My personal judgment says that maybe the high beam switch is to blame, but... is there any thermal circuit breaker in the headlight system, or something similar?

    Help greatly appreciated.

  2. #2
    Beater gonna beat sly's Avatar
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    Default

    I know there is, but I can't for the life of me remember where the breaker is. I no longer have the books associated with the 88 MGM I had to even give you a clue. It may be bad connection in the headlamp wiring harness as all that power does go through the headlamp switch no matter which system is switching it (autolamp or the manual switch). I've only ever replaced the switch in an 82 Lincoln Mark VI and a 92 Crown Vic. The switch in the Lincoln had sketchy contacts all through it. The Crown vic had a bad thermal breaker and that was for sure on the headlamp switch in that car. I remember seeing it. The headlights would work for a few seconds and then stay off for about 10 seconds and come back on. Replacing the switch fixed that one.

    In your case, the multifunction switch may well be the problem. The buzzing sound is troubling. That usually means a loose connection or bad ground or bad relay. The autolamp relay is a special breed of unobtanium (unable to get) for the years prior to 92. They used a 5-wire connector with a wire out the back of the relay to the metal clip for ground to trigger the coil. There is no replacement of those. Typical fix is to use a single dual pole single throw relay (switches two independent circuits using one coil) or two regular automotive relays to switch the two circuits. But that's only if the autolamp relay is having issues, but that doesn't seem to be the case for you.

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  3. #3
    I'm an air-conditioned gypsy gadget73's Avatar
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    Default

    I think the breaker is built into the headlamp switch, but I don't have an EVTM within reach to confirm.

    wondering if the buzzing is the autolamp relay. If there is a problem in the high beam wiring that is dragging the voltage down, it might be causing the relay to chatter, or possibly its arcing because of a short. Either way something isn't happy there.

    86 Lincoln Town Car (Galactica).
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