Started my truck up a few days ago, left blinker was fast. The front was working but not the rear, and the left brake/hazard wasn't working either.
Fuse 20 was blown but after replacing it, nothing changed. The bulbs are fine and there's no rust on the connectors.

I can't find what's causing it. Any ideas?

 

You didn't list your vehicle year, engine, etc so using a 2001 wiring diagram; check in BJB, fuse 6-15amp. In CJB check fuse 13-20amp and fuse 23-10amp.