Reverse light not activated put in Reverse gear

I would start with tracing the wiring from the bulb back to the switch which will be located on the top of the transmission if the wiring is good it is probably the switch. The best way to check both would be with a good volt ohm meter, the switch will be open when not in reverse and closed when in reverse that's where I would start anyway

 

I was a mechanic for 5 years before I started driving 10 years ago glad I could help

 

This is not going to be a misprint! I am guessing that you have a Columbia/Century? Did you notice that there is no fuse for reverse lights? It gets it's power from the air dryer heater circuit. First check the fuse for the air dryer heater. If it is blown, go to dryer and unplug 2 pin heater plug. If not, then start tracing wires as stated above. Good luck.

 

I had the dealer look at our 2012 model M2 with Allison auto because the lights wouldn't come on in reverse. Turns out, that if the truck is NOT RUNNING, with key on, the lights come on for only 10 or 15 seconds (not quite long enough for you to walk to the back of the truck) and then the BCM (body computer module) will turn them off. Start the motor, chock wheels and apply parking brake, select reverse, and like magic the lights are still on when you walk to the back of the truck. Apparently the lower voltage when the engine is not running causes the lights to draw more amperage and the BCM acts like a circuit breaker and kills the reverse light circuit after a few seconds. At least that's what the dealer told me. Might also apply to the class 8 trucks. . . . . or at least some variation of that.

 

Wouldn't the driveshaft tear your legs off?

 

Allison automatic. . . . . just sits there and idles while going BEEP BEEP