Mine failed under the original warranty, I recall that the latch was replaced (the switch is internal to the latch) and that the part wasn't cheap.

Considering that the other 4 doors on the car don't have "door ajar" warning lights, have you considered just bypassing the switch, rather than replacing it?

-BTC

'98 V70 T5 5-speed, 167k mi, front IPD stabilizer bar, rear factory HD bar, Bilstein HD, Volvo strut tower brace and skidplate, e-codes, XC grill, Lidatek LE30, V-1, Mobil-1 since new

"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." -- Douglas Noel Adams (1952-2001)

I appologize for the late answer. I just went and checked my tailgate. It could be the micro switch in the latch assembly. Make sure your interior light close to the tailgate is on after you open the tailgate. Then take a screw driver and close the latch, it should click twice. If the inside light turns off, then the micro switch is OK. Now close the door and check the inside light. If it is still on, the latch is not working properly.
I wrapped the U bolt on the bumper/body with electrical tape a long time ago, about 10 layers. The rattles were driving me nuts! If your molding is loose, consider buying a roll of carpet tape (2 sided) and cutting it a little narrower than the molding. Tape it down to the paint and then press the molding to the tape.
I also had a rattle because the door wasn't tight enough. I found a very thick double sided tape and put it on the body of the car where the molding touches, all the way down the side and across the bottom. I then covered that with colored electrical tape - no more rattles.
I hope I helped,
Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)