1968 XR7 with C4 will not crank via ignition key

Nice write up!

The neutral safety switches sold by Scott Drake are worthless. I got one and had the same problem. Got an NOS one on eBay and was able to adjust it and use it. One thing to watch out for, it can be installed backwards on the shaft.

Iā€™ll admit electrical is not my forte. Iā€™m confused by the conflicting signals Iā€™m receiving by the 2 NSSā€™s.
Old NSS gave me backup lights in the incorrect selector position. When removed, from trans, and just plugged in, I was able to crank the engine. New NSS, gave me backup lights in correct selector position, right from the start. Unable to repeat. Continuity in all three positions, no start. Daniel Carpenter NSS.

Are you clear that there are two switches. Neutral safety switch should show continuity only in Park and neutral. Reverse light switch should show continuity only in reverse.

Yes

Well I figured it out. Today I went over the original NSS. Using a multi meter, drill bit, blk magic marker, and a work bench, I marked a line at each place I had continuity, for Park, Neutral, and Reverse. I then connected it to the firewall, not the transmission, and turned the ignition key. Engine turned over. Yay!
Turned over at Park and Neutral marks. Reverse lights would come on and off. It appears that there is a bad spot in the wires where they enter the metal case of the NSS, Each time the case was moved or wiggled, Reverse light flickered on and off. I repeated the same process with the new NSS, and now I can start the car and have Reverse lights. I knew I was closeā€¦just had a hard time getting there.
New NSS is now mounted to transmission, and works.
Thanks for all the input, it does help.

Thanks for providing the update. In the future this is going to help a lot of people

Good job figuring it out! Itā€™s possible to get more use out of the old ones when the fail.
Here was a bad spot I found, when the backup lights only worked when wiggling the wires.

Thatā€™s interesting. I am going to hang on to the old for now, just in case.
Thanks for sharing.