I rebuilt the column shift on my 78 f250. I removed the B&M floor shifter and put the old NSS back on the transmission. The PO had laid the NSS on top of the C6 in the park position so the truck would start. The backup light sockets were shot so I replaced those. Just hooked them in tonight and my backup lights are on constantly now. In park, neutral, and drive. I have tried a different NSS I pulled from the JY with the same results. What am I over looking before I go buy a new switch? They are pricey new and I'm not convinced it's the switch.

 

B&M shifters have a nss and b/u switch on the shifter. Were there any wires connected to it? The PO could have them wired in somewhere other than the stock NSS.

 

No, the cable shifter was in place on its own without the light kit. The original switch was still in tact. It took me a few months to realize the lights didn't work.

 

I messed with it a bit today. When the switch is disconnected the lights are still on solid in all gears. So the sockets are getting switched power from somewhere else. I don't see any breaks in the wires anywhere. I can kill the lights by pulling the factory jumper wire in that little 90 degree socket with a white / pink and a black/ red wire. The wire diagram shows the white wire coming from the fuse to the switch. The black / red wire runs from the switch to the lights. What is that plug with the jumper in it for on an automatic? I understand the manual transmission would have a switch between these wires but it doesn't make sense in the automatic if that just supplies switched power directly to the lights. What am I missing here?

 

Some help from a fellow FTE member.

"When the trucks came with a manual trans, there was a dummy plug used to bypass the NSS switch. I've never been able to come up with a part number for the dummy plug. To bypass the automatic set up: Unplug the switch and discard or ignore. There are four wires in the harness plug, two each, red w/ blue trace and black w/ red trace. Run a jumper between the red/blue and red/blue, do the same for the black/red. That completely bypasses the NSS switch. Your truck will now start and the back-up lights will be permanently on.

Now on to the backup lights. In the engine compartment is a little U shaped jumper wire. It'll be located on the drivers side splash pan, just in front of the firewall where the wiring harness comes through. Unplug the little jumper, this will shut off the back up lights. There should be a back up light switch on the trans cover. Run two wires from the switch to the two wires that were jumped. This will get your back up lights working again.
Just a note, you could make a jumper plug out of the NSS. Cut the switch off the harness and splice the two pairs of wires. I just hate to cut these switches up. New, they're getting pricey. Here's the little jumper in the engine compartment.
EDIT: If you don't care about the back up lights, just jumper the red w/ blue trace wires. This will by pass the NSS but the back up lights won't work."

 

Thanks, I had seen that quite a few times after a bunch of searching. It's very strange that the circuit is complete without the switch plugged in. I'll have to trace the wires again and take readings at all the connectors to see where the live wire is. That little plug with the jumper cable still makes no sense to me. Power should be supplied on the white/pink wire from the fuse panel to the NSS switch where the Black/Red wire takes it to the lights when in reverse. Does anyone know where that little plug ties in? It's wires disappear into the harness tape.

 

Maybe this will help?

 

The grey harness clip for the NSS has double white/pink and black/red wires. One set goes to the black plug with that factory jumper. When the factory jumper is in it bypasses the switch and powers the lights up. If I remove the factory jumper from the black plug and jumper the wires on the NSS side of the clip the lights power up. This tells me both my switches have bad backup light functions. I still don't understand the purpose of that factory jumper.it seems like everyone's lights would be on constantly the way it is wired. I'll pick up a new switch tomorrow and make sure that is the problem.