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Thread: Diagnosing a missing low beam issue

  1. #1
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    Diagnosing a missing low beam issue

    Hi all, wondering if anyone might have some insight into an issue I'm trying to solve. If I depress the light button to the 2nd setting, I get no low beams. If i turn on the high beams, all 4 lamps light up.

    I've checked the voltage at both the relay, and the fuse, for the low beams. they both throw to +12V on a voltmeter when the button is fully depressed. So I have to assume the disconnect is somewhere between the fuse, and the lamps. Any ideas about how to go about sussing the fault? Thanks! You guys are super helpful here!

  2. #2
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    Quote Originally Posted by rjd2 View Post
    Hi all, wondering if anyone might have some insight into an issue I'm trying to solve. If I depress the light button to the 2nd setting, I get no low beams. If i turn on the high beams, all 4 lamps light up.

    I've checked the voltage at both the relay, and the fuse, for the low beams. they both throw to +12V on a voltmeter when the button is fully depressed. So I have to assume the disconnect is somewhere between the fuse, and the lamps. Any ideas about how to go about sussing the fault? Thanks! You guys are super helpful here!
    Does your green "low beam" indicator turn on?

  3. #3
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    Quote Originally Posted by dmcnc View Post
    Does your green "low beam" indicator turn on?
    no, i don't believe it does. is this in the instrument cluster? my left turn signal indicator in the instrument cluster is also out. got some wonkiness in there...

  4. #4
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    Quote Originally Posted by rjd2 View Post
    no, i don't believe it does. is this in the instrument cluster? my left turn signal indicator in the instrument cluster is also out. got some wonkiness in there...
    Follow the wiring schematics for your low beam (red/blue cable). For your low-beams I would start by checking the fuse 14.

    Headlamp.jpgDirectional.jpgDeLorean Wiring Schematic COLOR.pdf

  5. #5
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    Quote Originally Posted by dmcnc View Post
    Follow the wiring schematics for your low beam (red/blue cable). For your low-beams I would start by checking the fuse 14.

    Headlamp.jpgDirectional.jpgDeLorean Wiring Schematic COLOR.pdf

    thanks. i've checked the socket of fuse 14; when the light switch is engaged to the 2nd position, one side of it throws to 12V, so +V is arriving at the fuse. thanks for that diagram; i read alot of electronics schematics, but this one is a little...fuzzy, to me. i'll try to find a ground i can use as a ref for a DVM at the instrument cluster, and see if i can find the incoming voltage line at the turn signal area. thanks.

  6. #6
    Admins Never Retire Ron's Avatar
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    Quote Originally Posted by rjd2 View Post
    thanks. i've checked the socket of fuse 14; when the light switch is engaged to the 2nd position, one side of it throws to 12V, so +V is arriving at the fuse.
    Just in case , if when you said "it", you meant the fuse, note both sides should go to 12V+, else it is bad.....

    FWIW- The inner two bulbs are High Beam Only and the outer two have both High and Low beam filaments. So it is possible that both of the outer bulb's low beam filaments are bad...
    Jump 12V+ to the U/R (Blue/Red) wire right at a bulb to test them. If they're OK, chase the U/R wire back to the fuse...

    Seems it has to be one or the other.

  7. #7
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    Quote Originally Posted by Ron View Post
    Just in case , if when you said "it", you meant the fuse, note both sides should go to 12V+, else it is bad.....

    FWIW- The inner two bulbs are High Beam Only and the outer two have both High and Low beam filaments. So it is possible that both of the outer bulb's low beam filaments are bad...
    Jump 12V+ to the U/R (Blue/Red) wire right at a bulb to test them. If they're OK, chase the U/R wire back to the fuse...

    Seems it has to be one or the other.
    thanks. yes, only ONE side of fuse 14 goes to +12V. this is helpful! i have found several harnesses that were disconnected; the inner two bulbs were for some reason detached from their harnesses; i'll pull the outer bulbs and see what i can find.

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