I have a 98 110tdi with Gamma IV radio / cassette head unit (ref 3 B0 035 186A) which includes a cd control but without the changer. Purchased a cd changer (ref 1 J6 035 111) with lead (ref 1 J0 051 592A) on ebay for fitting in boot. The cable, however, has a mini ISO connector (blue) which doesn't match the connection on the back of the head unit - probably because the car is one of the last before the late 98 facelift? Therefore purchased an adaptor lead (ref 1 J0 051 445B) from dealer.
I've checked the changer in a more recent Passat and it works OK, but not in mine which is hardly surprising as there's no continuity of some of the wiring and the wiring colour codes don't match?
Anyone out there encountered / solved the same problem?