Dodge Ram

1998 Dodge Ram Pickup 2500 5.9 diesel, 5 speed manual transmission, 126,000 miles.
My back-up lights have quit. Checked both bulbs and
fuse using a multimeter. Removed switch to replace with an after market unit. When comparing the old switch with the new I noted the threads on the new unit were twice as long as the old. I also checked the old switch operation with a meter and it was functioning correctly. I did not install the new part for fear that the longer threaded area could damage the gear box. I returned the new switch to the seller and he was of no help finding another model.
Can you help?
February 22, 2007.

You probably got the wrong one. Take the old one in with you if need be.