Ok i got one for everyone! Just did an engine,trans and transfer case swap in my 97 blazer. Drive train was taken from a running 96 jimmy. The problem is with the key on, when you shift into neutral the engine cranks over without touching the key! If its already running and you shift into neutral it engages the starter. Where do I start to figure this out?
also it does it park to reverse

 

I assume that this is an auto trans?

Something is likely putting 12v on the purple/yellow/ppl=wht circuit from the starter position of the ignition switch to the starter relay coil. First pull the crank fuse in the ip fuse panel and see if this still happens. If so see if 12V shows up on the downstream contact of the fuse socket (the side that does not get 12v from the ignition switch going to start) when this happens. If this still happens with the fuse out crawl under the truck and disconnect the connector on the transmission range switch on the left side of the tranny and that should stop this from happening. If so, inspect the wiring and connector for damage or corrosion. Report back. I have never performed an exorcism before.

That range switch gets power on the pink wire from another fuse. I suspect that the switch is shorting that power to the starter line.


George

 

Thanks George! I'll check that all tomorrow and report back. And yes auto trans with floor shifter.

 

Ok i pulled the crank fuse and it still does it. Im positive its in the selector/indicator switch on the trans. My reverse lights are on in drive and park. Im betting i didn't get the switch lined up with the selector shaft.

 

That trans switch performs a simple switch function for start so with the crank fuse pulled there should be no source of power on that circuit from the downstream side of the crank fuse through that switch and on to the starter relay coil. I suspect that switch because it happens when you shift gears but we still need to figure out why 12v winds up on what should be a dead line with the crank fuse pulled. IOW, just an alignment problem would only cause a no start condition when the ignition switch puts 12v on that line and the trans switch does not close. We will be looking for a short to power somewhere. Unplugging that switch and checking again is the next step. If that doesn't do it then we will need to further isolate the problem until we find the short.


George

 

That trans range switch has power running to it from fuse 16 in the IP fuse panel on a pink wire. I suspect that a fault has shorted that power to your start circuit. Besides getting under the truck to disconnect that switch, pulling that fuse with everything hooked up will give us more info to diagnose.


George

 

Thanks for your help! The switch is broke and someone used black permatex to put it back together! I temporarily zip tied it together and everything works the way it should. I have a spare switch on my jimmy.

 

Another happy customer!

Glad you found it and I am glad that you went with proper diagnosis and avoided the parts cannon.

George