You need to get a good tester and start checking wires,check for power and then follow the wire back to find out why there is no power.
Look for the easy stuff first,broken wires ,smashed wires and worn thru wires from rubbing,wires are not easy ,a good book on your car will show where the wires go and make trouble shooting it much better.
Who knows what has been "rigged" over the years ,thats the reason for the book.