OK, I feel pretty silly on this one. I removed the trim from under the rear window and I don't see anything that looks like the main relay. The closest thing to a main relay I see is labeled as "retractor control" so I assume that is for the headlights. I downloaded the 91 service manual from here and where it shows the main relay should be, next to the ECU if I remember correctly, I have two really small relays, one behind each seat.