doubtfull a problem with voltage then, i take it the battery light comes on with ignition then goes out when car running?
id be looking at the earhts next, the cl motor has an earth point behind the passenger side doorcard.
fuse 21 does both the sunroof and the central locking though, so I'd take it out and check it with a multimeter. ive seen em go with a hairline crack thats difficult to spot