Hi I have a 2008 XC70 that has a problem with the brake lights. When the brakes are applied the brake lights on the hatch light up but not on the body of the car, but if the hatch is opened up the brake lights go out on the hatch and the brake lights light up on the body of the car. I only noticed this after I had picked up a camper trailer that had a round 7 pin trailer plug. As I only have a flat 4 pin plug installed on the car I bought a conversion plug that will connect a 4 pin flat plug to a 7 pin round plug. I checked the voltage in the 4 pin flat plug and there is no output when the hatch is down and there is when the hatch is up. I went back to the store that did the hitch and wiring install and they tried completely removing the trailer wiring and the problem still exists. I don't know how long this problem has been there as I only checked it after I hooked up the trailer. I have owned the car since 2010 and the hitch and wiring were installed in the fall of 2010. I have only towed a ski do trailer which uses a 4 pin flat connector 4 times since this was installed. Also there are no messages on the dash indicating anything is wrong.
Thank you in advance for your help