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Problem with dome light-help!

Discussion in 'Chevy Trucks' started by yardsmith, Nov 10, 2008.

  1. yardsmith

    yardsmith Senior Member
    Messages: 248

    Hey guys & gals
    Got an 88 1 ton dump GMC, & I've been fixing up the little things getting ready for winter & plowing. The dome light doesn't work, & I tried replacing the bulb. Nada, so I put my voltmeter to it, & I have a constant 6 volts! Whether door is open or not, & whether I turn the light switch knob for interior lights, it doesn't affect it. The under dash light works with the doors & light switch, but the dome light stymies me..... please help!!
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    They're supposed to be constant hot. It's when you supply a ground (via the door switches or switch) that the dome lights illuminate..

    Should be more than 6 volts on the orange wire though...should be full batt voltage. :nod:

    Likely the ground wire (should be white) going to the overhead dome is broken or corroded somewhere. Usually break somewhere along the floor from years being stepped on and damp after years of use.

    If you pull the sill plate off and pull any mat or insulation up you will be able to follow the dome wires from where they exit the B pillar all the way to the fuse box (the orange at least). The white wire will break off and head to the door switches and headlight switch, so you can follow it as well.
  3. yardsmith

    yardsmith Senior Member
    Messages: 248

    well I dug out the wiring- halfway up the wall it cnnects into a clip- I have 12 volts there- 3 more feet to the end of the wire where the light hooks up, I only have 10-11 volts. When I start the truck up it goes to 12 volts, but playing with the light switch / dimmer makes the voltage fluctuate, like the dimmer may have worn contacts or something. I may replace the light switch is need be-thoughts??
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Did you check the white wire for ground too?

    If the orange wire has any voltage at all (within reason) the dome light should come on....if it's getting a ground signal from the white wire of course.
  5. yardsmith

    yardsmith Senior Member
    Messages: 248

    yeah I had the voltmeter probes (pos on orange wire & neg on white wire) & got the voltage reading, then put the wires on both ends of a dome light bulb, & then on the wires of an aftermarket dome light I want to hook up & got zilch from both!! Do they have to be mounted/ grounded to the truck to light up??
  6. sechracer

    sechracer Senior Member
    Messages: 478

    When it gets the ground to the truck is when it will light up..... if you test the White wire from the light to the body/frame when it "should be grounded (light on), you probably have no continuity... thus a broken ground....

    Try this.... Using a jumper wire, touch the white wire side of the light with one end of the jumper, then ground the other end of the jumper and it should light. That tells you the white wire is broken somewhere.