Factory brake wiring is often not very good. Wire size too small, connector type bad choice, wires rubbing against metal, etc. If you do need to fix anything, you might consider making improvements rather than just "patch" it back like it was. If you've got a single axle trailer, having only one brake remaining is not good!
Proper operation of brakes on a trailer are extremely important. As mentioned, lift a wheel and see what happens when brakes are applied (pull breakaway pin but re-install right away when done). Manually adjust the brakes through the backing plate as needed. Also adjust the brake controller as per manual.
Actually, if it were me, I'd pull a drum off to see how the brakes look inside. It's so simple to do providing you can jack one wheel up at a time by putting a jack under the U-bolts. (Don't do that without a wood block under the U-bolts tho.)