burnt03

2007 NBS Silverado - truck lights work fine - plug into trailer, signal left or right and both trailer lights flash. - tried diff trailer, same thing. - Truck/trailer plug connectors are good. - unplugged the connectors under the bed (back of 7 pin, 4 connectors at main block under bed). Big pin at back of 7-pin was a bit corroded, sanded down, cleaned out and greased. Same thing. - nothing odd under there (ie. new damage that could’ve pinched wires) Ideas? Pull loom and check all wires for cuts/frays/corrosion? Is there a specific ground at that rear block that I could check? Thanks