Reverse lights and Neutral Safety Switch

[Jason Bourne]

I searched the site and found a lot of good information on the NSS. The reverse lights on my sons truck do not light up. I unplugged the reverse light connector from the NSS. I measured 12V on the dark green wire. I then jumpered the dark green and light green wires together and the backup lights came on so I know my issue is with the neutral safety switch.

It was getting dark so we decided we would look into it more on another day. We left the reverse light connector unplugged. When my son went to leave the truck wouldn’t start. Does the dark green wire provide power to the neutral safety side of the switch? I know the neutral safety switch circuit is the purple wires that get plugged into the NSS. My initial thought was these 2 circuits would be independent of each other.

My son plugged the green wire connector back in and the truck started. It’s possible that when doing that he bumped and moved the NSS or the purple wire connector, and that is why the truck started.

From searching through the other threads I know we need to try and loosen the screws on the NSS and slide the switch around to find the sweet spot. I’m nervous about messing around with a 50 year old brittle plastic switch. In case we end up breaking the switch can you jumper the purple wires together to bypass the neutral safety and start the truck? Do you have to supply power to the purple wires from the green wire?

Thanks for any help.

[dmjlambert]

Originally Posted by Jason Bourne

...plugged the green wire connector back in and the truck started. It’s possible that when doing that he bumped and moved the NSS or the purple wire connector, and that is why the truck started.

I think that's what happened.

Purple is for start, green is for backup lights. They are not related.


You may find a wiring diagram handy. Here's one. https://67-72chevytrucks.com/vboard/...27#post9186727

Year-specific wiring is in the service manuals. I recommend paper manuals, but PDF here for most years.
https://67-72chevytrucks.com/vboard/....php?p=5781194

[RustyPile]

The NSS is actually two switches with two independent circuits. The ignition switch sends power to the purple wire when in the START position only. The NSS portion of the switch interrupts the current flow to the starter in all positions except neutral and park. The other part of the NSS is for the backup lights only. With the ignition switch in the ON position, it provides power to certain circuits on the fuse box. The dark green wire at the NSS comes from the fuse box and the light green wire goes directly to the back-up lights..

After disturbing the NSS, the starter wouldn't engage because the slight movement put the switch out of (your words) "the sweet spot"... Normally, when the NSS is out of adjustment, starter doesn't engage AND the backup lights don't work.. You might try adjusting it, but probably the switch is bad...

[pjmoreland]

It could also be that the shifter linkage is out of adjustment. You should only be able to shift between neutral and drive without pulling back on the shifter, and you should have to pull back on the shifter to shift out of park. If needed, the shifter linkage should be adjusted before adjusting the NSS.

[Jason Bourne]

Originally Posted by RustyPile

The NSS is actually two switches with two independent circuits. The ignition switch sends power to the purple wire when in the START position only. The NSS portion of the switch interrupts the current flow to the starter in all positions except neutral and park. The other part of the NSS is for the backup lights only. With the ignition switch in the ON position, it provides power to certain circuits on the fuse box. The dark green wire at the NSS comes from the fuse box and the light green wire goes directly to the back-up lights..

After disturbing the NSS, the starter wouldn't engage because the slight movement put the switch out of (your words) "the sweet spot"... Normally, when the NSS is out of adjustment, starter doesn't engage AND the backup lights don't work.. You might try adjusting it, but probably the switch is bad...

Thanks for the confirmation. From everything I read on the threads on this board I thought the circuits should be independent. It just threw me off when the truck didn’t start with the green wire connector unplugged.

Haven’t had the truck long but it has never had a problem starting until we started troubleshooting shooting the backup lights. I’m thinking of trying to adjust the switch. Not sure if it’s possible for the switch to be adjusted for the neutral start but be out of alignment for the reverse lights.

Since it is just a simple open closed switch, if something goes really wrong when adjusting and we can’t get the neutral safety side to close again at least I can jumper the purple wires together as a temporary work around.

If we can’t get the NSS switch adjusted for the reverse lights but it does work for the neutral safety I’ve considered wiring the backup lights to a toggle switch in the dash. There is already an empty hole in the dashboard from something that was done to the truck over the years. I could be wrong but it looks to me that installing a new NSS on the column could be a real pain.

[Jason Bourne]

Originally Posted by pjmoreland

It could also be that the shifter linkage is out of adjustment. You should only be able to shift between neutral and drive without pulling back on the shifter, and you should have to pull back on the shifter to shift out of park. If needed, the shifter linkage should be adjusted before adjusting the NSS.

Good information. I’ll check that.

[pjmoreland]

If it's just a matter of adjustment to get your reverse lights working, then you should be able to get the reverse lights to come on by moving the shifter lever slightly one way or the other away from reverse. If the lights never come on in any position, then the issue is with your NSS. I had a NSS that had a broken housing which caused it to work intermittently. I had another NSS that was just old and crusty, but I was able to get it working again by disassembling it and cleaning and lubricating the contacts. You can also just get a new one for $20 on Amazon.

https://www.amazon.com/ACDelco-D2217...s%2C150&sr=8-2

[purple gas]

bypassing the neutral safety switch is a really really bad idea. It's amazing how quickly real bad **** can happen.

[sixty8HDC30]

You guys have a NSS?
The truck is more capable without one.
Safety third

[Jason Bourne]

Originally Posted by purple gas

bypassing the neutral safety switch is a really really bad idea. It's amazing how quickly real bad **** can happen.

I would only bypass it as a temporary measure to get it out of my driveway and into the street until we could get a working switch.

[Jason Bourne]

Can anyone who has installed a new NSS comment on the difficulty level for getting a new one aligned and installed properly. The space to install looks tight and visibility low.

[HO455]

It's not too bad. Unless your a big guy. A stickman like myself fits OK under the dashboard.

Now if I remember correctly I used a mirror to see into the slot (in the column,) while moving the shift lever into neutral. Once the detent was centered I dropped the switch tab in and put the bolt in and snugged it up finger tight.

Then I put the shifter in reverse and checked that the back up lights are on. If not then move the switch side to side as needed to get the lights to work. Then tighten the bolt and test the start function in park, neutral, and in gear. Adjust as necessary to make sure it won't start in gear.

[Jason Banks]

The hardest part is getting the screws started, like HO455 says, the adjustment is pretty easy.