The 1989 online factory manual has a very good electrical section, with wiring diagrams and wire connector and harness locations and routing, and circuit diagrams keyed to the harness and connector diagrams, with connector diagrams that show which wire is which in each side of the connector. It also shows you how to read and use all these diagrams, and to trace sircuits, locate shorts, blown fuses and burnt fusible links, and how to test relays and components. You need at a minimum an auto 12v test light, cheap ones are a couple of bucks. A good meter and knowledge of how to measure voltage and resistance/continuity is most useful.