AH, #20, thought I was focused looking at that panel. That's the fuse I blew on my daughter's rig not realizing it was Hot all the Time, not through the Key. Have you verified it's not blown? You can pull it and test across with a meter or use that ice-pick test light and another source, like the battery. Don't just inspect. Test to prove it's good. While it's out, you should find +12VDC on one pin of the fuse socket or the other.
That 20A is the Fuse I'd suggest replacing with a Breaker. I forget the formula but I think you should protect at about 15A per Trailer Axle. A site like Tekonsha should be able to confirm that.
Back to it, once you confirm power at #20 and Fuse/Breaker is good, you should also see it come on go on one terminal of the Brown connector (not Gray, I always Bet on Bryan) as you remove/insert #20. Then another terminal should light as you apply the coach brakes. Third terminal should test as Ground, and the last one should test OPEN. It's for the Blue Wire back to the 7-Way.
