If you look at the picture dome light and switch are part of the same unit. have never even been inside a wagon but... according to wiring diagram should be VERY close to the light. so maybe pulling the tailgate apart is not the answer...

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1996 s10 zr2 with a 6.5 turbo diesel
1996 c2500 suburban with a 6.5 turbo diesel
1981 300sd with a turbo 617
Monte carlo figure 8 car