Hi,  the 4 Star I bought had an old small round plug with an adapter to fit the newer style plug on the truck.  This was unreliable and would loose connection.   So we tried to put a new 7 prong end on the trailer and of course we can't get the job done.  Does anyone know the function of the wires?  We have black red brown yellow white and green.  No blue.  Thanks Joan

Here's some info on wiring colours:

http://www.etrailer.com/faq-wiring.aspx

Gard

On a 4-Star , it is the following;

Brown, running lights - Red, brakes - Black, ground - White, 12v auxiliary - Green, right turn - Yellow, left turn.