I have trailer wiring issues on my 2000 GMC Sierra Z71. It has the tow package with a 7 pin trailer plug. I bought an adapter to the 4-pin flat connector that my trailer has. When I put on the brakes the running lights go out; with the lights on and a turn signal on, the wrong light blinks and all of the running lights flicker. The trailer works fine on my '80 Chevy with a standard 4-pin plug. The dealer I talked to said it's probably not the truck but rather the adapter I bought was bad, so I bought one from them and it still doesn't work. Any ideas? Do you need a convertor since the brake lights and turn signals on the truck are seperate?

Any ideas would greatly be appreciated!!!

You should not need a converter on this truck. Does the trailer plug have the ground wire hooked to the frame of the trailer, is it clean? It sounds like a grounding problem

Problem solved, it was a grounding problem! The ground tab on the back side of the plug-in was green with corrosion. Once I cleaned that off everything works great. Thanks!!!