Trailer electrics blowing side light fuse

Hi guys, I have a 1986 defender 90 an whenever I connect my trailer electrics it blows the fuse for my side lights, I recently changed my headlights and wired in LEDs to the side lights but it is fine until I connect the trailer, any ideas if it is likely to be connected to the new head lights or a separate problem with the trailer electrics?

Trailer - otherwise it would blow all the time as the trailer sockets (on the fender) are always live.