I have a 2000 Caravan with trailer hitch, wire harness intalled after market. Everything works fine (signal, brake lights) when the head lights are turned off. When I turn the head lights ON, the trailerbrake lights come on and stay on and the trailer turn signal does not flash behind the trailer either (the van brake lights/turn signalcontinue to work fine, everything is fine once I turn the van headlights off). My other vehicle works fine with the trailer so it must be something in how the wiring harness was hooked up in the Caravan?

 

Are you using a converter box to power the trailer lights? On the 1996 and up Caravans, you cannot hook the harnes wires directly to the tailights. You can buy these convertors on line or at auto parts stores--they cost around 35 to 60 bucks.