Just finished doing a TKO600 5 spd swap into my 1974 454 Vette. I hooked up the battery earlier today to make sure all the electrical components worked correctly. I also wanted to bump the starter to make sure I had it installed correctly as well. I had yet to install the neutral safety switch on the new tranny so I needed to jump the purple/purple-white wires on the switch for the starter to work. To my surprise, the starter cranked with the key in the ON position and not the START position. Rather than crank a new engine over and over, to test things, I have been using a multimeter on the purple wire of the NSS to see what was going on. With the key in the ON position AND the START position, I get a constant 12 volts at the purple wire. I did some trouble shooting and unplugged the 2 connectors on the ignition switch. Naturally there was 0 volts at the NSS. When I plugged the white connector back onto the ignition switch, the starter operated normaly (0 volts in the ON position and 12V in the START). However when I replugged back in the black connector on the ignition switch, I get a constant 12V at the NSS with the key in ON or START. I had the steering column out to install the new clutch pedal, but dont think I disturbed the position of the switch. Thoughts?

 

Since you had the steering column out, I suspect the ignition switch needs adjusted.

 

I don't know if this is going to help much, but a manual transmission, 1974 Vette does not have a neutral start switch. It should have a clutch switch. The backup light switch should be on the transmission or the shifter linkage.

Here is how you synchronize the steering column to the ignition switch.
The ignition switch on the steering column has five positions. They are as follows:
From full clockwise back ccw; START, RUN, OFF, OFF-LOCK, and ACCESSORY.

Remove the switch from the steering column jacket. You should be able to see a slider on the underside of the switch. You should also be
able to insert a small allen wrench or other type of small tool to reach into the switch and move the slider to various switch positions. It may feel quite stiff as you move the slider.

You now want to place the ignition switch in the OFF position. You do this by reaching into the ignition switch and moving the slider all the way to the end of travel to the ACCESSORY position. It should detent and stay in that position. If in doubt, the other extreme will be the START position and you will feel a spring return.

Now move the slider two detent positions back from the ACCESSORY position, this will place the switch in the OFF position.

Your 1974 steering column will have a lever on the lower end next to the lower steering column bearing. Push the lever down to any position. Place your ignition key in the START position and now rotate your ignition key CCW until it stops. That will be the OFF position. Now you have both the steering column and the ignition switch in the OFF positions.

Carefully fit the actuator rod into the ignition switch slider hole and attach the ignition switch to the column by lightly tightening the two fasteners. Lightly push the switch down the column (away from the steering wheel), to take out lash in the actuator rod, and tighten the fasteners. Caution should be exercised to prevent moving the switch out of the OFF detent. Tighten the fasteners to 35 in-lbs.

 

I had that happen wires were crossed when I bipassed the nss. It would start in run position.

 

Thanks for the responses! I will do some work on it today and get back.

 

Turns out it was the NSS itself. With the purple wire unhooked from the ignition switch, the purple wire at the NSS was still getting a constant 12V with the key in the ON position. The NSS switch was getting power from a purple/yellow wire hooked up to what I believe was the starter interrupt relay. Removed the NSS completely and now everything works fine. Thanks again for the help.