The rear door lock microswitch is part of the lock assembly, but I think that you can take it out and replace it. Once you have the microswitch out, hopefully, if you can find out it's rating, you can get the same one from electronic part store.

If you car is a wagon, the first step to remove the tailgate panel is to get extra tailgate panel clips from dealer. These clips are around the panel and are very easy to break during the removal. Then, you pry the cover around the tailgate latch (inside the car) with a putty knife. It is very tight and need force to pry the cover out. Once the inside latch cover is out, then you grep the bottom edge of the tailgate with fingers and then pull it down a little bit. Then you pull the panel toward yourself with the bottom edge still down. This should unlock the clips of the tailgate, and please do the removal carefully. Once the panel is off, you will see the lock assembly and wiring.

Good luck.

Ching-Ho Cheng
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1995 855 NA, Bilstein Strut & Shocks, Volvo Protective Grill, K&N Filter, E-Code Lens, Alpine CD-Changer, AutoDim RearView Mirror, 6000K HID