Most likely, the back up light switch located on the steering column has failed. Bypass it to see if the lights come on.

 

Yea, I just put a switch under the dash so if I need the back ups I can flick the switch. Sometimes the stock switch is just out of adjustment.

 

the lights come on in the middle of park and reverse and then the back up lights go off.
will check the back-up switch..thanks

 

Switch needs adjusting. Sounds like it is out of position.

 

My car does the same thing. It doesn't come on when you put it in reverse but when I move the shifter a hair past reverse headed towards park they come on. How do you adjust this?

Dave

 

Have someone move the gear shift lever from park to reverse to drive then back while you watch the action at the column mounted switch. After a few cycles, you should have a pretty good idea which way to move the switch. Also, while it is in reverse, see if you can determine which way the switch needs to move in order to make contact the actuator.

 

spoonplugger gives good advice

If you can actuate the switch by hand and the light come on, then you know that the electrical is working fine.
All you need to do is adjust the swithc in its holder till it is actuated by the mechanism at the appropriate time.
Good Luck