Hello Andrew and welcome to the forum. Cleaning connectors and earths is a very good place to start. I have produced a colour wiring diagram for your model, see here for details, I can send you a pdf version for £1.00 or a printed and laminated A3 copy in the post for £7.50 plus £5.00 p&p. Let me know if you would like any further information.
Best wishes Chris
MGCGB Branch Liaison Officer