One of the simplest things that might appear and happened to me was that the big 80A fuse in the relay was not held down tightly.

The screws were finger tight giving a lot of resistance across their fastenings. A lot of resistance occurred here caused local heating and finally ruptured the fuse. Searching for the blown fuse revealed the finger tight contacts and a $1.00 fuse brought us back to normal. Just a possibility
David