Hitch Rav4

Joes Hitch & Trailer in DFW installed 7-pin trailer wiring on my 2006 RAV4. Now 4 dashboard warning lights act up. A few minutes after starting the car the parking brake light, ABS warning, VSC, and traction control lights light up and remain lit until the key is removed. I figured a loose wire or inverted connection. Joe's looked and said the only fix is to remove the wiring - that it's a problem with proprietary Toyota technology. Today I decided to test the wiring with my trailer. Before I even connect the trailer, I grabbed the toungue and the hitch and it shocked me. I touched both again. Same thing. Touching each individually was fine. The shock wasn't always immediate. I did not feel long enough to tell if it was pulsing. I killed the ignition. There was still a voltage difference. I didn't hook up the trailer for fear of damage to the vehicle. Anyone had similar problems? Troubleshooting? Is Joe's correct that it's impossible w/o going to Toyota dealer ($800 installed)