Reverse lights

I have a 1994 4WD and the reverse lights do not come on. Anyone know where the switch is located that turns on the lights when the truck goes into reverse, or what else to look for to that may cause this problem.

http://personal.utulsa.edu/~nathan-buchanan/93fsm/manualtrans/30assembly.pdf

Look at this! It should help.

Thank you very much for the info. I'm going to give it a go tonight to see if I can't get them to work.