Here's some wiring diagrams for early models.
The RA29 diagram is very similar to your '79.
http://autos.groups.yahoo.com/group/...ng%20diagrams/
Pull out ALL fuses except the fusible links.
Put the fuses back in one by one and test that feature by turning it on.
That will narrow down the problem area.
The Haynes manual will be very useful - get it.
Also, get a cheap multimeter or at least a circuit tester.
The circuit tester is just a globe in a nice plastic pen-like case and a wire to attach to ground.
Attach the wire to the body and touch the end of the probe to something of interest - it will light up if the something has power to it.
Or do the reverse, connect the wire to +12V and then probe things to see if they are connected to ground.
- Stepho