backup lights

I have a 92 1500, 4.3L, 5 sp manual. My backup lights don't work. I used the factory manual to troubleshoot the problem and it led me to replacing the backup light switch which I did. The lights still don't work. However, if I remove the switch, and leave the wiring connected, the lights work when I press the switch. It seems to me that the switch isn't adjusted properly since it works but the lights still won't come on in reverse. The manual discusses automatic transmissions but doesn't mention adjustment procedures for manuals. There is another similar thread I know, but it doesn't say how to adjust. I am wondering how to do this and would appreciate any help. Thanks.