Changing the bearings is easy use the old ones to gently drift the new ones in.
I don't like wires running trough trailer chassis, fill the plug up grease (waterproof) is your best answer. This practice of running cables is quite common sur la continent.
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo