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Repeat electrical problem in F-800

Discussion in 'Ford Trucks' started by SLSNursery, Jan 7, 2001.

  1. SLSNursery

    SLSNursery PlowSite.com Veteran
    Messages: 140

    A while back I posted about some electrical problems I have had with a '97 F-800. One problem remains, and it seems to be eluding the dealer - who has been cooperative with me up to this point, but I am tired of second guessing their technician and wasting down time with the vehicle.

    No matter what we do - the headlights won't stay on. The switch is new and so is the entire headlight wiring harness. After about 10 minutes the headlights flash. Not the parking lights or other accessories, just the headlights.

    This leads me to believe the circuit for the headlights is a straight shot, not related to the fuse for the tailights or parking lights. A mechanic friend of mine suggested that there is a resettable circuit breaker inside of the headlight switch, that seems to keep tripping. Has anyone experienced this?

    When the dealer replaced the headlight harness I told them to leave the plow lights out of it, since they attributed the problem to the plow lights originally. We had to direct wire the plow lights through a totally separate circuit, and this has worked fine, and has its own fuse.
     
  2. Larrytow

    Larrytow Junior Member
    Messages: 28

    Phill, there is a circut breaker built in to the headlight switch. It resets itself automaticly. That is why the headlamps are flashing; the breaker is resetting all the time. You most likley have a direct short to ground in a wire from the switch to the headlamps. If not that, then maybe the wires to the dimmer switch or the dimmer switch itself. It also could be a weak breaker in the headlight switch. That is not as probbable as a short tho, however I have seen it before. A test light that shows hot and ground will make tracking a short easier. Unplug the switches and probe the plug; no terminal should show ground. If you find one that does, that is the wire to track to find the short.

    Regards, Larry
     
  3. GeoffD

    GeoffD PlowSite.com Veteran
    Messages: 2,266

    Couldn't have said it better myself. I will ask my mechanic tommorrow. We had a problem with head lights on an F 700 once.

    Geoff
     
  4. DaveO

    DaveO PlowSite.com Veteran
    from Ma.
    Messages: 299

    Flashing headlights

    Phil,

    I have seen some vehicles that have a relay to feed the headlights. Since someone stated that there is a breaker on the switch, I doubt there is a relay.

    I have a simple suggestion. Check the headlights themselves. I once had a customer's bike, that would keep blowing the fuse, but not right away. The problem was that he had "upgraded" the bulbs. They were a much higher wattage, too much for the fuse to handle consistently. This is probably NOT your problem, but is easy to check.

    Dave
     
  5. wyldman

    wyldman Member
    Messages: 3,265

    Check the ground circuit of the headlamps.They are on an individual circuit with no fuse,just the breaker in the headlamp switch.The headlamps are usually grounded to the rad support,which must be grounded to the battery.Usually it is a bad ground strap of some sort.If I remember correctly (it's been a while since i've seen a F800),the rad support is rubber mounted,and some of the front end parts are fiberglass and plastic,which does not conduct electricity.Use an ohmmeter,and check the resistance between the headlamp ground wire and the battery negative terminal (with battery disconnected).If it over five ohms,make a ground strap from the rad support (mounted to good clean metal) to the battery negative post,and it should fix your problem.The poor ground raises the resistance of the circuit,which drives the amperage up,thus tripping the breaker in the headlamp switch.Hope this helps.