Start with checking the CB they are all tied to. Make sure the black wire is connected all the way. Check white wire is connected to bus bar correctly.
From there move to junction box. Not sure where that will be located on your trailer. Refer to your other post in the FW forum. I thought you had a FW. Picture in that thread was in basement of a HT FW. We dont have any BHTS's on our lot right now or I would go look.
These things can get tricky. Since you have no power at all I am guessing you have a black wire loose somewhere.
Schematic below but be warned I have found these things not to be entirely accurate.