Usually an adjustment will do it. Loosen the two bolts holding the neutral start switch to the side of the transmission and give it a little turn to where it will start in P or N and the reverse lights come on in R. HOWEVER, a common cause of losing alignment is worn shift rod bushings. I'll bet yours are worn or gone. Replacing the bushings is a little tricky but there are lots of tips and shortcuts in them thar archives. Definitely something to check and fix before you touch the neutral start switch.

Sixto
95 S420
87 300SDL
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