1984 533i

Can anybody advise me on how to diagnose whether it is my starter or my ignition switch that is causing my car not to start?

Get a multimeter and disconnect the black/yellow wire that pushes on to the solenoid. IIRC, Bentley states that you need at least 10 volts on it when the key is turned. If this is ok, then the starter is dead. Good luck getting it out as it is a PITA to remove the top bolt. The factory 17-mm wrench is ideal for this task PLUS you will need a LOT of patience!

Thanks Jimmy.

Oddly enough... it decided to start right up today. Any ideas why it would be so temperamental?

Clean all your battery connections including the ground to body wire. These cars tend to get 'moody' as they age, also if you haven't done this yet replace all fuses with new ones and clean/re-tension the connections. As a preventive measure also, many people change the main relay and the fuel pump relay as they have been known to cause issues every now and then.

I am facing the same problem. i thing cleaning of battery and check all the fuses will solve the problem

I just had the same scenario happen to me yesterday, I went from thinking it was the fuel relay, motor would crank, fuel pump would thump, starter then didn't engage. I statred banging on the trunk with the jack to loosen up the brushed on the fuel pump. Then it occurrred to me I drained all the juice out the battery! I had someone jump start me and wammo started right up, all terminal are kept spotless too. I went a bought the prpoper size battery, the PO was a bit of a tard wrong size battery and he had disabled allot of stuff like the stock temp gauge, locking gas cap door etc...man was BMW waaaay ahead o it's time with the E28!