Sailteach2

Hello, I recently tried to hitch up a trailor to my A4 1.8 STI. The tow bar and electrics seem to be factory or professionally fitted. It is very neat, in fact so much so. I am having difficulty in deciding what is the tow bar wiring and what is factory original. The problem is there is no power to anything. The trailor lights are all dead and nothing can be made to work. I have checked the output socket with a meter and cannot find any life anywhere. I am at a loss as to what to try. I understand there maybe a relay but no sign of it. Any help would be most appreciated. Thanks in advance.