Hi,

Thanks for the responses so far. The trailers wiring harness is new. I installed it by soldering the cables and I used heat shrink tubing instead of the crimp on junk. When I test the trailers electrics, by running 12 volt to the individual pins on the plug /connector the whole system seems to work fine. I can basically simulate all the light functions the trailer should have. This is why I think the trailer is O.K..
Ground... I had the same concerns with bad ground connections, especially since I have on of those tilting style trailers, where the tongue is hinged to the rest. I decided to run the ground wire past the tongue to a permanently mounted piece of frame.

In the next days I might try to find someone who lets me hock up my car to a properly functioning trailer... will see if the problem is caused by my car!?
Does someone know about those converter modules (I currently use a Hoppy brand black box style module converter is integrated in the connector) ? Are there good and crappy ones? Which types should I avoid?

Thanks,

Patrick