If I were you David I would isolate the battery drain first. As you say it may well be the light switch module but could well be lots of other things as well. If you fixate on the LSM and get it recoded you may still have the problem to solve.
Nich.
Nicholas John Peter Tinker - # 484
Manufactured on Tuesday 27th April 2004 @ 12.17.47.
Commission Number: 24468.
Brochure Model: M3 Tourer 4.6 V8 260PS.
Specification Code: L01B.
CICode: D1511.
Trim Level: TL8.9 (M3).
65th ZT-T 260SE to be made out of 115.
11th ZT-T 260 SE in Pearl Black (PBT) out of 23 produced. Manufactured in the UK by MG Rover Group Ltd.
Undoubtedly the battery drain is my priority. I'll put a multimeter into play tomorrow and read the difference, if any, when the LSM is completely disconnected. If that is the source I'll obtain a replacement. It will be a relief if that proves to be culprit.