I have a 2013 Thomas C2,that seamed to go into test light mode when ever it felt like it. I removed the switch and everything was good. So I replaced the switch and it made it worse. turn the key on and it goes into test mode. And will not let me cancel it. anyone have any ideas of what I should look at.
Possibly wrong switch, wire rubbed through and barely touching, or corrosion at end connection. Try reinstalling old switch and see if you can cancel. Do you have the Freightliner software?
I agree with Tigger on the switch. The part number is on the side of the switch. TBB is notorious for having more than one switch that physically looks the same as another but is wired different internally.
Check all of the terminals on the connector for being pushed out of the connector body, I have found this to be a regular problem when reconnecting switches.