Why

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Ngtjest

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I have a 99 Yukon 4x4 all of a sudden the heat wasn’t working until I turned the headlights on and it redirected the vents from feet and defrost to vents and feet Why why haha if anyone has anything please let me know
 

east302

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Couple of questions...

Are you getting any warm or hot air at all?

Does air flow correctly correspond to the dial setting--floor, panel and defrost?

If your headlights are, literally, controlling the air flow direction and temperature, then I'd be looking for some kind of short or damaged wiring.
 
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Ngtjest

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My headlights are controlling everything air temp and direction it’s crazy was thinking maybe a wire is sharing a common ground or something but went to look and it seems the previous owner was a stereo guy and there are more random wires around then I was prepared for only saving grace is mostly capped off or taped
 

east302

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That sucks. Yeah, it has to be something crossed in there. It should be relatively easy to trace it from the a/c panel. Here's a diagram from a 1998, maybe it will help sort through the wires...



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