"check left rear tail light" displays in console but tail light is working normally, what's wrong ?

what year windstar is it?

2002

first,i'd unplug the trailer wiring and put the car back like it was to start with. check to see if your problem is gone. if it is,check the trailer wiring for a short. (nicked or cut wire) still there? check the car wiring,you might have nicked a wire during install. also check the bulb,they have been known to short one filament to the other and still light up. swap it to the other side,if the problem goes with the bulb to the other side,replace the bulb.

If all your lights are working (park, brake and hazard), then chances are the trailer harness is not the issue. More likely, you just need to upgrade your hazard switch with a heavy duty one. I am betting the one you have now is being overloaded,

I did try unplugging the trailer harness interface unit on the left side and connecting the van wiring directly to the lamps as it was before I installed the trailer wiring. This did fix the problem but when I plugged the trailer wiring interface unit back in place it still was working ??? The only thing I can guess is that there was a partial poor connection or high resistance in one of the plugs and unseating and reseating them made for a proper connection. Thanks to everyone who replied.