First, Has it always been this way or did it once work correctly???
If always this way, the installer used the wrong wire to feed hot side of t-stat and it is being broken when the wall switch is thrown. Since everything works when lights are off it is not a fuse. Since the t-stat draws very little amps, I would find another hot wire close to it and tap into it for power using an in-line fuse for safety. Might be easier than going crazy tracing the other circuit. (I thought the t-stat was supposed to get it's 12v from the A/C control board but I may be wrong) JM2˘, Hank
Be sure to let us know what you find.
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Hank & Lynn
2007 Cougar 290RKS, E-Z Flex, 16" XPS RIBs ( SOLD
.. Gonna miss her ... looking for new 5r)
2004.5 Dodge 2500 QC, LB, 5.9HO, WestTach gauges, Ride-Rite