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Old 04-07-2021, 03:31 AM   #1
chrismtb's Avatar
Join Date: Jul 2016
Location: San Diego
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Vehicle: 1988 D21 4x4 SEV6
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Default One lowbeam and one highbeam not working (not bulbs)

I'm having an issue where my driver side low beam and passenger side high beam are both out. I get one side lit in low and one lit in high. This is on a 1988 D21 Hardbody SEV6, standard bulbs.

I have replaced the bulbs and the problem sticks with the side of the car. E.g., if I swap bulbs between the 2 sides, the driver side low beam is still out.

When I check the voltages, I get 12-14 volts (depending on if the truck is running) across the appropriate terminals. On the driver side, that's between red/green to black for low beam and between red/blue to black for high beam. On the passenger side, that's between red/black to black for low beam and red/yellow to black for high beam.

Given the correct voltages, I'd guess that there's a weak connection or high resistance somewhere that is causing a voltage drop when a load is placed across it. I'd guess it might be the headlight or high beam switches on the steering column and I'd like to see if anyone has suggestions before I tear it apart.

One thing I see on the driver side is this random connector hanging loose on the wire to the headlight and I can't find anything it was supposed to connect to. Does anyone know what that is?

Last edited by jp2code; 04-07-2021 at 06:32 PM.
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