it's possible to repair the harness harness also. once you remove the top trim cover and expose the big terminal block, you can probe all the wires at each end of the harness and figure out which one(s) are bad. i did this on my wagon, not so much because i wanted to save the 100 bucks for the new harness, but because i had everything apart and wanted to fix it at that time.

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punkinfair

I'm just celebrating having all the electrics working in my 1992 300TE.

The soft close tailgate, rear wiper washer and centre stoplight stopped a couple of years ago.

It seems 90% of tailgate problems are with the LHS wiring as it passes through the grommet. When I removed the rear roof trim I found 4 wires that were obviously broken and then 3 others that were also about to fail. The other 6 tested OK.
I still can't believe that there's 13 wires going through that grommet!
After repairs and shrink wrap the toughest part of the whole job was pulling all the wires back through. I managed it 2 and 3 at a time with a wire coathanger hook that I kept covering in electrical tape to stop it ripping the grommet to pieces.

Good luck to any who try it. Good idea to search for a wiring diagram first as well.
Cheers
Stu
1992 300TE