Mice.
There are a couple of relays that are mounted right at the top's elctro-hydraulic unit in the trunk (immediately behind the left rear wheel). Easily accessible behind the felt side panel. I'd be looking for bite marks and bare wires touching each other.
Perhaps totally unrelated, but worth mentioning, is that I had an old (1975) Surburban, and every few years the turn signals would stop working. Replace the flasher, and all would be good again__for a while. One of the times, I took the flasher apart, and it was so jam-packed with (dead) ants, that it was forcing the contact closed. Must've been something in the insulating varnish that those ants just had to have! Mice are attracted to the vinyl insulation in the same way (soybean is one of the ingredients in PVC).