I've been messing with the lights on my 78 bronco with a C6. The neutral safety switch works, it will only start in park or neutral.
As soon as I turn on the key, the reverse lights are on. If I understand correctly, the NSS and the reverse are in the same switch on the side of the transmission.

Another issue I have, is the left rear blinker works, until I turn on the headlights. Then it won't flash. I've read that is a grounding issue. I cleaned the grounds, no change. I ran a wire directly from the battery to the ground strap in the taillight housing. No change. It is a new bulb housing as well, but maybe the ground circuit in it is bad? Anyone have any other place to look for the culprits?
On the plus side, I discovered I have tilt steering. And after owning this bronco for 2 years, I fixed the vacuum operated heater controls. The PO had unhooked the vacuum for some reason. Now I have heat at the floor and the vents instead of just defrost.

 

Yes the C6 has the NSS and reverse light switch down on the side of the trans. Has the wiring up under the dash been messed with? Was the truck originally a manual trans? Congrats on the tilt wheel discovery, just know that if you need a new TS switch you have to get a tilt wheel one. You blinker issue might be a TS switch problem because the wiring is up in the column/under the steering wheel. Or even a head light switch issue.





This statement is to help with trouble shooting."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."

 

It was originally a C6 transmission. Yes, wiring has been messed with.
i unplugged the NSS in the engine compartment, and i still had reverse lights on all the time (key on). Somewhere, some wires must be shorted together.

 

Does the right side work correctly?

If yes, I would suggest to make sure the left side brake lights (dual filament) and taillight (single filament) wiring from the new plug to the factory wiring are not crossed.

It is possible the new socket is bad but wouldn't be the first place i would look. you can also test these circuits with a multimeter of course.

 

Yes the right blinker works with and without the headlights on. I will inspect the wiring of the socket and add a ground strap to from taillight to frame and a new frame to battery ground.

Both reverse lights are on when the key is on, with and without the NSS plugged in. For now I put the temporary red tape over the reverse light so I don't get stopped for that.

 

So I partially fixed my problem. The left blinkers NOT working with headlights was my wiring of the new socket. I thought I wired them the same as the one I took off, but I had swapped the brown and black. They look so similar on the 46 year old wiring.
i did also.add a couple grounds. And fixed the engine to body ground that looked in poor shape.

Reverse is still on both sides as soon as I turn the key on. And ideas where this might be coming from?

 

Been there, done that.


sorry can't help you out with the NSS..assuming it's wired hot and then grounded when in reverse by design? if so, then i would take a close look at the switch itself to see if there is wear on it causing it to ground in all positions.

 

I was having some weird light issues with my '79 last year when I was getting it running after it had sat for some years. Initially I thought it was the right front turn signal socket, due to a very redneck engineered fix I found when I took it apart (see picture below). I replaced the socket with a new one, and was able to get my right front turn signal working, but then the side markers started flashing when I activated the t/s and intermittently the lights wouldn't work at all. Decided to pull out the side marker on the right front and saw some haze inside the bulb, yet the bulb was still working, decided to swap it out for a new bulb because of the discoloration and all the issues went away. So perhaps you have a bad side marker bulb?

I think I would try swapping bulbs, if they show any hint of discoloration before tearing the column apart to replace the t/s switch.

I don't think that will help with the b/u light situation though. The last truck I had with a C6 I ended up swapping over to an NP435 and adding the wire loop up on the firewall so I could get the truck to start after unplugging the NSS. I think I would check the wires from where the NSS plugs in on the firewall down to the NSS itself and see if any insulation is broken causing crossed wires. I am not sure if there are any adjustments to be made on the NSS itself, but you might check for that too. If you have another rig with a C6 that you can pull a NSS from and try it to see if the b/u lights stay on that would help determine if you have a bad NSS that has an internal short.

 

To follow up and finish this thread, I found the problem with the reverse lights. It was the 90 degree- 2 pin plug on the drivers side near the firewall that Rich has a picture of above. The previous owner had jumped this plug. By unplugging the pins, now my lights work as intended, only when in reverse. I never knew the reverse lights were jumpered before, because the sockets were bad.

 

Never mind me ............