Adding a neutral safety switch

[Johnl48]

I converted to an automatic from a 4 sp. I'm using the original harness, so I know I have to reroute the reverse light plug into the cab but what do I need to do to add a wire for the neutral safety switch ?

Thank

[Steeveedee]

Neutral Safety switch (NSS) power comes from the ignition switch. If you had a manual with no switch, you will need to run the purple wire from the ignition switch to the NSS, then from the NSS to the starter. Doesn't have to be purple if you're the only one who works on it, because you will know. But I'd run it all purple in case someone else is driving it and you aren't available to fix it.

[damnyankee36]

I've never owned a manual trans truck so I'm assuming there was no clutch pedal-mounted safety switch. Find a good spot to cut the purple wire under the dash that goes from the ignition switch to the starter solenoid. Route and/or extend the ends to the backup lights/neutral safety switch on the column and connect them there.

Again, I am assuming that you will also be using an auto column to mount the switch. I guess all manual trucks didn't have any switch mounted on the column?

[Johnl48]

Originally Posted by Steeveedee

Neutral Safety switch (NSS) power comes from the ignition switch. If you had a manual with no switch, you will need to run the purple wire from the ignition switch to the NSS, then from the NSS to the starter. Doesn't have to be purple if you're the only one who works on it, because you will know. But I'd run it all purple in case someone else is driving it and you aren't available to fix it.

So this wire gets cut and attached to the switch ?

[Thealien]

On my 1972 blazer that is a factory four-speed vehicle the two purple wires in the harness come out about the same place they would on an automatic. There’s a small plug plugged into it with a purple wire looped back to itself. So in order to connect it to an automatic neutral safety switch I would just have to unplug the loop and plug the connector into the neutral safety switch on the column.

[Thealien]

I want to add that this picture is from an M and H replacement harness. I can’t imagine they would make completely different harnesses for automatics and manual transmissions.

This is a picture of the connector I mentioned in my post above. I have it on top of the steering column so it doesn’t get damaged with the break or clutch pedal since it is not attached to a switch. I’m not 100% sure if the factory did it exactly like this or if they buried that connector in the harness?

[Steeveedee]

Originally Posted by Johnl48

So this wire gets cut and attached to the switch ?

Yup, that purple one.

[Johnl48]

Originally Posted by Thealien

I want to add that this picture is from an M and H replacement harness. I can’t imagine they would make completely different harnesses for automatics and manual transmissions.

This is a picture of the connector I mentioned in my post above. I have it on top of the steering column so it doesn’t get damaged with the break or clutch pedal since it is not attached to a switch. I’m not 100% sure if the factory did it exactly like this or if they buried that connector in the harness?

Mine doesn't have that plug

[Thealien]

Originally Posted by Johnl48

Mine doesn't have that plug

Follow the wire from the ignition switch it exits the cab at the bulkhead connector. It would probably be easier to cut it down there if you are sure that connector isn’t buried somewhere.

[71CHEVYSHORTBED402]

Originally Posted by Thealien

I want to add that this picture is from an M and H replacement harness. I can’t imagine they would make completely different harnesses for automatics and manual transmissions.

This is a picture of the connector I mentioned in my post above. I have it on top of the steering column so it doesn’t get damaged with the break or clutch pedal since it is not attached to a switch. I’m not 100% sure if the factory did it exactly like this or if they buried that connector in the harness?

Same and agree.

Some notes I took that may be helpful. Gauges are sometimes a guess. Heck even color, I'm color blind but did some research, mostly

The brake light switch wires are one 18 AWG white wire to the turn signal switch, and one 18 AWG orange wire from the fuse box. The harness runs from the RH side of the fuse box and wraps with the neutral safety/reverse switch harnesses.

The neutral safety/reverse lamps switch harnesses run from the RH side of the fuse box and plug into the switch as:
• The plug with two 12 AWG purple wires connects to the switch’s RH terminals for neutral safety.

• The plug with two 18 AWG light green and two 18 AWG dark green wires connects to the switch’s LH terminals for reverse lamps, with the light green wires positioned on top.

The wires are taped together with the brake lights switch wires, and there’s an in-harness clip that plugs into the firewall adjacent where the fuse panel reads CLSTR. FEED.

Corrections welcome

Some really good threads:
http://67-72chevytrucks.com/vboard/s...d.php?t=592968

http://67-72chevytrucks.com/vboard/s...d.php?t=801374

[pjmoreland]

You could pop the purple wire out of the bulkhead connector on the firewall and plug it into the Neutral safety switch. You could then get some more purple 12 gauge wire and a couple of Packard 56 crimp terminals and make a short wire to run from the other terminal on the Neutral safety switch to the bulkhead. This approach saves you from having to extend or splice any wires. You need to use the two NSS terminals that are parallel and close together. I believe this is the correct connector housing.

https://jcaparts.com/collections/bui...ator-pin-black

These are the crimp terminals (select 12 gauge for purple wires and 18 gauge for green wires).

https://jcaparts.com/collections/che...-awg-18-20-awg

This should be the reverse light connector housing in case you want to tackle that issue as well. I believe you would pop the light and dark green wires out of the bulkhead, pop them into this housing, and plug it into the NSS.

https://jcaparts.com/collections/che...-housing-black

[Johnl48]

Originally Posted by pjmoreland

You could pop the purple wire out of the bulkhead connector on the firewall and plug it into the Neutral safety switch. You could then get some more purple 12 gauge wire and a couple of Packard 56 crimp terminals and make a short wire to run from the other terminal on the Neutral safety switch to the bulkhead. You need to use the two NSS terminals that are parallel and close together. I believe this is the correct connector housing.

https://jcaparts.com/collections/bui...ator-pin-black

These are the crimp terminals.

https://jcaparts.com/collections/che...-awg-18-20-awg

This should be the reverse light connector housing in case you want to tackle that issue as well. I believe you would pop the light and dark green wires out of the bulkhead connector, pop them into this housing, and plug it into the NSS.

https://jcaparts.com/collections/che...-housing-black

Your links don't work

[pjmoreland]

I fixed them