While testing the wiring for trailer lights I realized my reverse lights on my 79 F150 400/C6 weren't working. All other lights work. I found that the wiring for my neutral safety switch had cooked from the exhaust (explaining the smell I recently noticed) so I cut the wires near the switch and ran wires up to the engine compartment, this time routing them clear of header heat. So, I still don't have reverse lights. Am I wrong about the neutral safety switch controlling the reverse lights? Maybe the switch is burned out and needs to be replaced but I'm looking for the free repair this time. I need to buy new rims, tires, and springs for my rear end upgrade and that leaves no money for anything else. Thanks for any help

 

No, you're not wrong, the NSS also controls the backup lights.

I would use a volt meter and see if there's actually voltage down there....

 

check the fuse for it mite be blown

 

i had same problem with my 78 ( 400 C6 ) and i replaced my NSS because i could start my truck in any gear and i had also read that the NSS controls the reverse lights...unfortunately they still dont work.

 

my reverse lights do not work either. i have to trace it back farther.

 

There are definitely a few things that can cause this, but you guys seem to be on the right track.

Check the fuse

Check the continuity within the NSS at the plug when the shifter is in reverse. I have also read somewhere that some people have pulled the NSS apart and cleaned the contacts inside the NSS with good results, but I looked and can not find it again.

Check the bulbs and sockets (the sockets can look good, but be bad. I had to replace a couple on my truck even thought they looked good)

There is a plug behind the rear bumper that gets some heavy corrosion sometimes. Check it, clean it or replace it if necessary.

Check the grounds, make sure all connections are clean and tight. Battery to engine, engine to frame and cab, cab to frame, bed to frame.

 

For your troubleshooting pleasure.....Here you go:

74-78 Wiring Diagram Pt1

74-78 Wiring Diagram Pt2

Zoom in and it should be readable.

 

Yep, just have to start at the source and see where power cuts off for good. Simple as that.

 

Thanks for all the replies. I had already the bed harness and it ohms out. I also checked the fuses and I don't have any blown fuses and from my shop manual it said the same fuse controlled other lights. Unfortunately the shop manual doesn't speak much about the NSS other then adjusting it.....not fixing it or any other electrical problem associated with it. I need to do more investigating. I ran out of day light after I fixed the burnt wires and haven't had time to take another look. I've checked and the lights don't come on in any gear, but the thing is specific about which gear it is in to start. I would bet the switch burned out. Maybe I can find one at the junk yard. I need to get a driveshaft so I'll already be under a rig for that. Are they hard to change and adjust?

 

If your not in a hurry, I get home from work Thursday evening and I think I have a good NSS off of an older C4. I think the body of the NSS is the same, it just has a different plug, You could splice your plug onto it. I know I will not be using it, I could have it in the mail to you on Friday. If your interested, shoot me a PM.

Can anyone confirm that the main body, mounting and function is the same for the NSS's for the C6 and C4?

If it'll work for you, it's yours.

EDIT - The one I have at home is a MOTORCRAFT Part #SW877 {#C9ZZ7A247B}

 

I looked this up on Rock Auto's site, they say it was installed on Mustangs & Cougars in the mid to late 1960s.

I have no idea what else it may fit....

 

Correct. I had it on a C4 behind a 302 in a 2wd 68 F100. The engine and tranny were not the originals, so I really do not know what year everything was. But I do know it looks similar to the one listed for the 79's with a C6 other than the plug.

 

fuse for back up lights is same one used by the wipers

 

Had the same problem with a truck (96 f150) where I used to work. The NSS can't really be repaired (at least that one couldn't) and autozone doesn't sell them because its a dealer part and an expensive one at that. But its safe to say thats your issue.