1990 GMC Sierra vechical electrical problem

1990 GMC SIERRA
105,000 MILES • V8 • 2WD • AUTOMATIC
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CODY14011
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I bought this truck and when i turn on the headlights i loose my turning signals and taillights. The blinkers work when the lights are off. i obviously only can drive during the day. I also had an 89 chevy with the same problem. I wouldn't think it would be a coincidence I bought two vehicles with the same problem, other people had to encounter such issues. Do you any ideas as to what if causing this. I changed the entire steering colunm and nothing changed. It is driving me nuts, any help would be greatly appriciated. Thank you
Sam
Nov 15, 2009 at 1:13 PM
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JDL
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https://www.2carpros.com/forum/automotive_pictures/170934_gmc_headlamp_1.jpg

Welcome to the forum, if the headlamp switch is on the dash and the dimmer is on the steering column, there should be a multiwire connector under the dash close to steering column, for circuits going to and from the steering column. You should be able to test voltage circuits there, using a testlite. Your headlamp switch probably has two circuits, one is a circuit breaker, only for the headlamps, red wire carries voltage for that. The other circuit is a fused circuit for tail lites--dash lites and stuff. orange wire carries voltage for that. You can also see that the yellow wire carries voltage to the dimmer, I believe. At the headlamps themselves, lite green wire is voltage for high beam. Tan wire is voltage for low beam.
Nov 15, 2009 at 1:36 PM