I am having trouble getting the trailer lights to work via my truck. The trailer is brand new, fine and working (was hooked up to the delivery guy's truck and all was ok). The wire harness extension from my truck was really old, so I replaced it yesterday, but it's still not working. That lead wire harness connects into a type of t-connector, which also connects what I imagine are each of the taillights. The taillights and brakelight for my truck work fine. Any possible diagnosis? Do I just need to replace the connector, or could the problem run further up the chain? It's a '95 F-150 with a 4-wire harness if that helps at all.