Neutral Safety switch with a twist.

[Missourimark]

My 69 long horn has a wiring short I can’t figure out. First when I bought this truck a couple months ago I started cleaning up the wiring, 50 years of hacking and adding accessories. I found out I didn’t have a neutral safety. They had bypassed it with a wire from the ignition to the starter. So I hooked it up the correct way and found a no start issue as they probably did then they just ran a wire to remedy the problem. When wired correctly it has a dead short , like dim the dome light dead short. Run a jumper no issue starts fine. So easy enough replace the neutral switch which I did, same issue no start , dead short again. Run a jumper, starts fine. What am I missing ?

[Steeveedee]

Wiring is the biggest PITA ever. You are going to have to trace it all out to find the problem. The Start circuit is pretty straightforward, though. Power goes from the ignition switch through the fat purple wire to the neutral safety switch, and continues through the fat purple wire to the solenoid. Just follow it out until you find the problem. I'd bet money that the fat purple wire is clamped between the engine and the transmission, or the insulation is melted and the wire is stuck to the exhaust manifold. Seen 'em both happen.

[Ironangel]

The neutral safety switch is adjustable...Did you adjust it? Might just have to loosen the switch and tweek it a bit...Steeveedee brings up a good point in locating the short.

[Missourimark]

Yes I did adjust it correctly, the back up lights come on in the correct position and I found no continuity to ground on the switch itself. It looks like Sunday fun !

[VetteVet]

If you have no continuity on the NSS to ground then Pull the purple wire plug and check the wires for continuity to ground. The one from the key switch should be OK unless the key is shorting it at the key switch, not likely because it didn't on the jumper wire. The other one is probably the grounded one. It runs from the NSS to the firewall block behind the fuse panel, and through it to the starter solenoid.

Your no start issue when wired correctly means the purple wire is open to the starter solenoid, but the dead short means it is grounded to the block or the exhaust or pinched somewhere like Steevedee said. It should be easy to find just follow the purple wire where it comes out of the firewall block and goes toward the starter. I think it runs along the top of the firewall in the rain gutter and across to the right side down to the starter.



If you separate the firewall block by removing the bolt in the center, you can isolate the cab from the engine side of the wire, and see if the continuity to ground goes away from the cab, then you'll know the ground isn't in the cab.

If it goes away from the engine side then you'll know its inside the cab. If you pull the fuse panel you can see the purple wire inside the cab and you should be able to see where it's grounded.

[Rich69shortfleet]

New reproduction wiring harnesses can cure these kinds of issues with no muss, no fuss. You might not need both underdash and engine side if you can figure out which side of the firewall the problem is on. However, if the harness(es) are hacked up as bad as you say, simply replacing them wholesale will save a lot of problems now and later. I've even had good luck with solid unhacked used harnesses, though those are getting harder to find and you have to first find a truck that has all the same accessories you have or want (gauges, no gauges mostly) and then hope you can find a good one. So, again, reproduction harnesses save a lot of trouble in the long run.

[Missourimark]

After further investigation I may have found the culprit, the purple primary wire was cut and replaced with a 16 gauge wire over top the engine . I believe the wire was to small for the amperage draw for the solenoid to actuate . The neutral safety switch has amperage loss there to . So bypassing it would allow enough amperage for the solenoid to work. Replacing 16 gauge with 10 gauge wire.