You should definitely invest in a Bentley Manual for the E30 - it's got detailed electrical wiring diagrams and good descriptions, pictures, diagnostic tests, etc. It costs ~$40, but if you're trying to do anything yourself, it's a must. Dont' get a Chilton or other brand...they're not as comprehensive.
I've done a bunch of work on my E30...some of it having to do with the fuel pumps (there are 2, an in-tank pump, and a main fuel pump). All the relays are in the relay box on teh driver's side under the hood...or just outside of the relay box.
Get the Bentley - it will answer 90% of your questions.