ive just got some rear lights delivered off ebay and they are different to the ones on my m-reg 405 glx, the lense part doesnt fit over the bulb holder so i used the bulb holders that came with the new lights, which works fine...

the plug fits but are the wires in the same order?

hope this makes sense!!

Ph1 and 2 ones are different, the lenses anyway.

I found a problem when I changed over the tail lights from a '92 P1 onto an '89 P1. Everything fitted fine but the foglights came on when using the indicators, plus a few other strange combinations (of which I can't recall atm).

Not sure if there's some way you can tell before hand, you may have to try it with a mate outside the car checking what's happening.