2008 630 tail light stays on with truck off

I recently purchased a 2008 volvo 630 it has ved 12 motor eaton 10 speed autoshift 358 rears .The truck has traction control system
It had a tcs abs light on .The dealer sad it was a switch in the steering wheel when I got it back the left taillight
would burn very dim only 2 of the leds would light up.When the truck is running the lights do what they are supposed to do
I took it back they had it 3 days and said it was fixed they said it was a bad air switch
Here a couple of days later the light is on again .I am wondering if anyone has had this problem and if anyone has the wiring diagram for this truck

thanks

 

The truck is wired for grote lights .It had a trucklite with a adapter on that side I put a grote light back in and now it is off