The Stovebolt Site Forums The Shop Area The Electrical Bay Key switch failure or neutral safety switch fault?

I just bought a 66 GMC sub and started going over wiring for the rear lights and found all had been removed from the plug near the gas tank. I got tail/brake/turn lights working properly. Sub was factory automatic, yet PO removed the 351 v6 and tranny and installed 350/350 THM combo. I found the backup lights to work, when the switch was moved to a certain point on the column. I could not get the lights to operate in conjunction with the tranny in reverse. I even tried moving the switch while the engine was running, with the tranny in reverse. After several attempts, I created a new problem. Now the engine cranks and fires off when the key is moved from off to run position, sometimes. The other half of the time, I can turn the key to run and gauges act correctly, but when the shifter is moved to reverse, the engine fires up. This is my first automatic to mess with. Not totally familiar with NS/BU switch. I figure it's a problem with the NS/BU since that is what I was messing with when the problem started. I have been troubleshooting equipment all day at work and after two hours of chasing and correcting wiring, so I kind of gave up for the night. Will start fresh in the morning, I just wanted to pick a few brains. Thanks for any information.

Fresh start and found the problem first thing when I removed the NS/BU switch. New switch, problem corrected.

Do your backup lights work now?

Yes, they work as they should. Thanks.