1999 F150 4x4 Backup lights not working.
 

This has been a problem for awhile. They failed completely, but no blown fuses and applying voltage to the Positive side of the backup lights, they will illuminate when jumpered. Suspecting the Multi-Function switch on the transmission that is suppose to also control the brake lights, I replaced it but no change. They still don't work. Any WAGS or suggestions?

Well my first suggestion would be to post in the 97-03 forum, as this is the 87-96 forum :)

But I think you are probably on to something with the way the tranny is delivering the signal to the lights - good luck.

I installed a Backup Camera on my 94 F150, I found the switch on my M5OD wasn't working. I tried two new switches from the local auto parts and couldn't get them to work. The switch actuator just wasn't being depressed enough to make the contacts. I finally had to find an original at a wrecking yard now they work fine.