I have a 95 GMC Sierra 1500 2wd 5 speed manual trans

the reverse light are not working I tracked it down to the switch so I installed a new one but that didnt help, I removed the switch and when I push on the ball the lights go on but when its installed does nothing so what ever is internal is not doing its job

is there an adjustment or some thing inside the trans?

I'm not 100% sure but I think its the NV3500 trans

thanks