try connecting a positive wire to a positive socket connection for he tail
your problem is likely a bad plug assembly, a direct connection from the ba
ttery positive should brighten things.....
in fact the one connection will likely brighten all lights
trailer plugs are cheap, you could make up a test plug with light bulbs, an
d plug it into the tow vehicle......
or make up a test tow vehicle end connection to power the trailer, add a sw
itch or two to duplicate brake lights etc
but i would still suggest rewiring the total trailer, you will find trouble
s, corroded contacts, poor connections, and in the case of one trailer i wo
rked on the main traler wire insulation was badly worn, in a hidden area it
would of shorted and taken out all trailer lights..... found when pulling
if you rewire go at least one size heavier......
if the wire is 16 gauge, go to 14 gauge, it will be stiffer, but work bette
r...... of course use straded
the last trailer i worked on, the trailers plug assembly connected inside a
small metal box on the frame. taking the cover off revealed its backside w
as rotted out, allowing water coirrosion of the connections....'the damage
wasdnt visible from the outside
you should seal all crimps with blobs of silicone caulk all around every co
nnection so water cant get at them....