Back up lights have their own local ground to the bedsides behind the housings. Same as the taillights. If he had no ground at all the lights wouldn't be on. He may be grounding to another source, but that wouldn't be affected by the headlights.
The rear harness (6 wires w/o side markers) runs to the first X member on the frame, and plug into a 4 wire harness that runs to the cab. In the cab they run to the firewall and to the fuse block where they run to the back-up switch.
You have to have some sort of short between the fuse block and the back-up switch somewhere. Did someone hack up the dash harness at all?
The reason I ask is you have to make sure a green and yellow are your lead and ground for the back-up lights. If anything else then you're getting power from another source, like your headlight circuit...
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'69 3/4 ton C20 2wd w/ 350ci/400THM and a wood bed!
'69 3/4 ton Custom 20 2wd w/ ORIGINAL 350ci/4sp Manual and a wood bed (parts beast).
Seattle, WA.
*See pics of my trucks and project at
www.webshots.com!
[This message has been edited by new69owner (edited April 10, 2002).]