Neutral Safety Switch wiring - The 1947 - Present Chevrolet & GMC Truck Message Board Network

OregonNed · 05-23-2018, 10:34 AM

My truck started life with a manual transmission, which was replaced with a TH-350 by a previous owner. I've seen what I believe is the wire that used to go to the transmission - hanging disconnected and taped down near the bundle that goes from the firewall to the starter. It is a purple wire. Now I am getting ready to install a floor shifter (new) with a neutral safety switch - (the old shifter did not have that option). What is the best way to newly wire the new switch?

davepl · 05-23-2018, 10:57 AM

The purple wire is the wire that carries current from the ignition switch to the starter solenoid. So any interruption of that circuit will act as a neutral safety.

Wire it to the provided neutral safety in the new shifter and you should be set!

I strongly encourage you to solder and make any connections in this wire PEFFECT, including any old cuts or splices from previous owners. If the purple wire is anything but perfect, you'll find that NOTHING happens when you go to crank it on a hot day.

That's the famous "Chevy Starter Heat Soak" problem and people throw starters and heat shields and all kinds of parts at it, but it's usually just a bad connection in the purple wire.

**VetteVet** · 05-23-2018, 12:03 PM

Here's a diagram showing the wiring of the start circuit.

Name: solenoid01.gif
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Just follow Dave's advice and add the purple wire from the NSS to the S terminal on the starter. If you have the HEi distributor you won't have the coil wiring from the R terminal.

OregonNed · 05-23-2018, 12:17 PM

Thank you. So since the wire (purple) is not connected to anything now, there must be another wire supplying voltage to the solenoid. I am guessing I would trace out the wires, make sure purple is good from its source, connect it to the switch and then from there out to the solenoid?

vinro · 05-23-2018, 01:13 PM

The purple wire would need to be cut and connected to the NSS.
Check this thread...
http://67-72chevytrucks.com/vboard/s...d.php?t=755946

OregonNed · 05-23-2018, 01:25 PM

Thank you, that helps too. Slowly but surely getting all the wiring in this thing back to specs! Ned

*randy500* · 05-24-2018, 01:30 AM

If the truck is starting then some wire is connected to the solenoid (originally it was purple) but it doesn't matter.
What matters is that the key switch has a purple wire that engages the starter.
The purple wire from the key switch is the wire to interrupt for your neutral safety switch on your floor shifter.
Cut and extend that wire to your switch on the shifter.

05-23-2018, 10:34 AM	#1
OregonNed Registered User Join Date: Dec 2012 Location: Vancouver, Washington Posts: 1,644	Neutral Safety Switch wiring My truck started life with a manual transmission, which was replaced with a TH-350 by a previous owner. I've seen what I believe is the wire that used to go to the transmission - hanging disconnected and taped down near the bundle that goes from the firewall to the starter. It is a purple wire. Now I am getting ready to install a floor shifter (new) with a neutral safety switch - (the old shifter did not have that option). What is the best way to newly wire the new switch? __________________ 1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop

05-23-2018, 10:57 AM	#2
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Neutral Safety Switch wiring The purple wire is the wire that carries current from the ignition switch to the starter solenoid. So any interruption of that circuit will act as a neutral safety. Wire it to the provided neutral safety in the new shifter and you should be set! I strongly encourage you to solder and make any connections in this wire PEFFECT, including any old cuts or splices from previous owners. If the purple wire is anything but perfect, you'll find that NOTHING happens when you go to crank it on a hot day. That's the famous "Chevy Starter Heat Soak" problem and people throw starters and heat shields and all kinds of parts at it, but it's usually just a bad connection in the purple wire. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible Last edited by davepl; 05-24-2018 at 12:14 PM.

05-23-2018, 12:03 PM	#3
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,719	Re: Neutral Safety Switch wiring Here's a diagram showing the wiring of the start circuit. Just follow Dave's advice and add the purple wire from the NSS to the S terminal on the starter. If you have the HEi distributor you won't have the coil wiring from the R terminal. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

05-23-2018, 12:17 PM	#4
OregonNed Registered User Join Date: Dec 2012 Location: Vancouver, Washington Posts: 1,644	Re: Neutral Safety Switch wiring Thank you. So since the wire (purple) is not connected to anything now, there must be another wire supplying voltage to the solenoid. I am guessing I would trace out the wires, make sure purple is good from its source, connect it to the switch and then from there out to the solenoid? __________________ 1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop

05-23-2018, 01:13 PM	#5
vinro Registered User Join Date: Jan 2018 Location: america Posts: 99	Re: Neutral Safety Switch wiring The purple wire would need to be cut and connected to the NSS. Check this thread... http://67-72chevytrucks.com/vboard/s...d.php?t=755946

05-23-2018, 01:25 PM	#6
OregonNed Registered User Join Date: Dec 2012 Location: Vancouver, Washington Posts: 1,644	Re: Neutral Safety Switch wiring Thank you, that helps too. Slowly but surely getting all the wiring in this thing back to specs! Ned __________________ 1968 Chevrolet C/10 LWB - 327, TH350 - 4/5 Drop

05-24-2018, 01:30 AM	#7
randy500 Account Suspended Join Date: Jul 2016 Location: Tacoma, WA Posts: 6,873	Re: Neutral Safety Switch wiring If the truck is starting then some wire is connected to the solenoid (originally it was purple) but it doesn't matter. What matters is that the key switch has a purple wire that engages the starter. The purple wire from the key switch is the wire to interrupt for your neutral safety switch on your floor shifter. Cut and extend that wire to your switch on the shifter.



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