Need help with neutral safety switch wiring

[Roger Carter]

Hello All,

Helping a friend get his '81 F-100 short narrow bed running and on the road. He purchased the truck as a rolling shell and has installed a 302 / C4 combination in the truck. The truck was originally an automatic truck, unsure of original engine or transmission. The truck also had factory cruise control, but that is not being reinstalled on this new engine.

I have researched this site, and others, but have not found the information I am looking for. I am unable to find the wiring for the neutral safety switch in the truck's wiring. The wiring diagrams show the nss mounted on the transmission, in typical Ford fashion, but doesn't address the chassis wiring for it.  I have a nss on the transmission but nothing to connect it to. Other Fords I have worked on had a tail coming out of an engine compartment wire loom that the nss and backlight switch would connect to. Typically this tail was in the middle of the firewall. This truck does not have this tail, and the loom appears to run into the cab near the heater, with no tail for the nss.

I have read, on other sites, that the early 80's F-series do not show a nss, according to the Ford parts books. The parts books may not show a nss, but I am sure that would be an error in the book.

I am aware the nss interrupts the "hot in start" wire between the ignition switch and solenoid and am able to wire the switch as such, but would like to locate the original wiring and tie into it.

Any help to locate the original nss wiring / tail would be appreciated.

Thanks in advance,

Roger Carter

[PetesPonies]

Are you ABSOLUTELY sure it was an automatic trans from the factory?

[Gary Lewis]

Roger - There does seem to be an omission in the 1981 EVTM, but the 1986 EVTM does show the NSS on Page 30 in the Start & Ignition section. Better yet, on Page 35 you can see where C128 is along the side of the driver's side frame.

I'm pretty sure the 81's had an NSS as Dad's truck did/does and so did Rusty, and both are 81's. So I don't know why it doesn't show in the EVTM.

The only thing to watch out for is that in '81 Ford used hash marks and dots on some of the wires, but in 1986 they replaced those with stripes.

[PetesPonies]

If you look at the small wire on the solenoid, you should see the wire that goes to the NSS.

[Roger Carter]

I am as sure as I can be that the truck was originally an automatic.

The steering column appears factory and is an auto column. The the bell crank shift linkage appears to be in place and original to the truck.

Thanks for the response.

[Roger Carter]

Thanks, Gary.

I did see what you are talking about in the '86 EVTM and did notice the hash marks, dots, etc. on the wiring of the '81. I have connectors in the vicinity of the transmission inside the frame rail on the '81. I did a check previously and did not see the nss wiring though, I will check again and take a closer look.

Thanks for the suggestions.

[Roger Carter]

Thanks for the input.

 I was aware the solenoid trigger wire (hot in Start) is the wire the nss interrupts. I just can't locate the ends of the wire that connect to the nss wiring. I was hoping to locate the factory wiring / connector since I really didn't want to start opening wire looms. If that is what it comes to, so be it. Just not my first choice.

I appreciate the response.

[Gary Lewis]

Don't miss Page 31 saying C128 is a gray connector near the dual brake warning switch and that it had 18 connections - which seems a lot more than I remember.

[PetesPonies]

Wasn't expecting you to open harnesses, but to look for that color up by the firewall. If it was standard  trans truck, that connector would be used to get power to the clutch pedal switch. But if it was an automatic, the connector has to be exposed. Look for that color near the brake master cylinder/firewall area.

[JimsRebel]

The wiring for the NSS located on the C6, exits the main harness near the base of the brake booster, on my 1986 F150. It travels down the left frame rail about a foot. You will see a 4 wire plug that connects to the very long pigtail of the NSS / backup light switch mounted left side of the C6. I am not sure if the C4 is in the same location.

I am not completely convinced my truck will not start if I disconnect this connector. As my truck is an Auto, the column has a mechanical lockout to keep the key from rotating to the start position unless the gear selector is in Park or Neutral. This lockout means you don't need a NSS with an auto column.
Jim

[PetesPonies]

I'm convinced . .try it.

[Gary Lewis]

I know the early trucks, like through '81 at least, didn't have a clutch lockout switch, so it would be possible that the autos didn't have an NSS.

And while I said Dad's did, I'm not sure that is correct. As Jim pointed out, if you can't turn the key it shouldn't be able to start.

[85lebaront2]

Gary, on Darth, the NSS was on the side of the C6, between the shift lever and the downshift lever. Older models with the FMX had it on the column as there was no place on an FMX, Castr Iron Cruise-O-Matic or Ford-O-Matic for one, C4s used essentially the same switch, the AOD has a plunger switch in the case. Yes, the key mechanism is mechanically interlocked, but the NSS also controls the back up lights, and shifters can get out of adjustment.

FWIW, I had a good friend that was killed by his wife's Explorer he was working on for his granddaughter. He thought the NSS was bad and was underneath jumping the starter, switch was good, Explorer was in reverse and backed of the ramps crushing his chest when he tried to roll out from under it as it started moving.

[Gary Lewis]

Yep, that's where the switch was on Dad's C6, but now I'm wondering if the truck only used the backup light portion thereof.

Man, that's awful about your friend. My father taught me a healthy respect for vehicles being lifted off the ground, so I am extremely careful. But after seeing that maybe I need to step it up another notch. 🙈

[PetesPonies]

Autos have had a NSS since there were automatic transmissions. True, clutches didn't have switches . . .  but we dumbed it down for the masses  :)  I have still, many cars/trucks with no switch on the clutch. I always started a vehicle my depressing the clutch, same with motorcycles. CSS is just another thing to go bad, IMO. But hey, it's been around for a while, I remember when it started.

[Roger Carter]

Hello All,

First, a thank you to everyone who has posted a comment. I appreciate the help.

I had a chance today to get back to the truck in question. I thoroughly checked the underside for plugs, connectors, wiring tails, etc. Found one plug and connector near the cross member, it was a factory 2 wire plug and connector, and from the colors it appeared to be the back-up light wiring. These wires were in their own loom, with no other wires. Tracing the wires rearward, they went to the back of the truck. No bed or lights on the rig yet. Going forward, this loom ran into a piece of convoluted wire loom with one other wire loom. Tracing this second loom to the rear, it had the sending unit wire for the fuel tank and carried on to the back of the truck with tail and turn signal wiring.
There were no other plugs, connectors or wire looms tucked inside (or outside) the driver side frame rail.

I didn't have a chance to follow the convoluted loom into, or to do any digging for wires in, the engine compartment. Hopefully that can be a chore for tomorrow. Previously I had done some looking, but had seen nothing with the correct colored wires. Will need to dig deeper.

As for attempting to start the rig, that is a couple days away. I don't have an issue with starting it without a NSS, but do want to avoid any catastrophic accidents. I want to be certain the truck is safe when I return it to its owner.

There does seem to a mechanical interlock between the key switch and the shift lever, with the key being able to be removed only when the shifter is in the PARK position. I doubt this would be used in place of a NSS, but will have to do further checking.

The trans in the truck is a C4 from a early 70's Mustang, and the NSS is the same, or very similar to those on a C6, as described by previous posters. The switch is a combination NSS and back up light switch, with four wires coming from it.

Beginning to think the '81 EVTM was correct in not showing a NSS in their diagrams...

Thanks again for all the comments, hints and suggestions. I will post my findings as I dig deeper.

[ctubutis]

Roger,

I think you just answered your own question...

There's an interlock in the column that disallows turning the key to START when equipped with an automatic transmission and the selector lever isn't in PARK or NEUTRAL, this should eliminate the need for a NSS, no?

1981 manual-trans trucks don't have a clutch switch so it wouldn't surprise me if there aren't provisions for a trans-lever switch (seeing as how there's a mechanical block that does the same thing).

The backup lamp wiring is black/pink IIRC.

[PetesPonies]

wow . . . .  he he OK if you think that.

[ctubutis]

PetesPonies wrote

wow . . . .  he he OK if you think that.

well that's a friendly, helpful response

[Gary Lewis]

Roger - I'll pull the harness for Dad's truck out tomorrow and see if it has the NSS connector. I'm thinking like you that the 81's didn't have it and the EVTM is right. But I'll find out.