So.... driving home last night I notice my anti-lock brake light is on and the little trip computer above the rear view mirror is not working. I go to shut it off,pull the key and the truck keeps running !! I put the key back in and now it won't let me take it out of park.I remove the key again and it is still running.I pull the ECM/Batt fuse and the truck stops running.Fuse is blown,I replace it.Truck is now on as if it is running. I step on the brake and the truck shuts down,I let off and it turns back on,mind you there is no key even in the ignition during all this.I disconnect my battery so it will power down and go to bed. Today I reconnect battery and everything is still the same..... WTF ??

 

So your blazer installed a gas saving mod to its self..? when youre on the brakes the engine is off but when youre off the brakes the engine is on? GENIUS!

Joking aside.. Im going to state the obvious and say you have a short if the fuse blew. But the problem is where.. I know the ignition switch will cause a lot of weird things and is a common problem on these trucks, although ive never heard of it doing this. Im not sure how you would test it before replacing it but that would be my first guess.

 

Thanks....yeah that's the problem, I have no idea where to even begin trouble shooting.

 

Anatomy of the ignition switch

There is a link to how the ignition switch works, and how to test it. I would just pull it off and look at the contacts, but im not even 100% sure if the ignition switch would cause this problem, its worth looking at the ignition switch just for grins tho, to see the shape its in.


It really sounds like the ignition switch is the problem tho, because that is what should be telling the truck to turn off, and if you can pull the key out of the IGNITION without it turning off then i would guess something isnt contacting right. And it wont let you take it out of park because i would guess because the switch doesnt think the ignition is in the 'run' position. Thats just what makes sense to me... but idk why the fuse would be blowing.

But if there are problems going on with your blazer that cant be described its generally the ignition switch because it sends power to everything.

Hopefully someone will have more info on this.

 

I'm betting that you have some melted wiring somewhere that is feeding into the system. Your only course of action is to dig into the harnesses until you find the problem.

 

I will start searching for the short tomorrow. Thanks Gentlemen. Any idea where to start? Come to think of it I pulled a trailer yesterday and of course plugged in the trailer lights.... the connection did feel a little warm when I disconnected them ???? huh..

 

^^^ Listen to him.

I was kinda thinking that as well, but i thought the ignition switch was more likely. So you're saying that probably isnt a possibility at all? (for future reference)

 

Not that it isn't a possibility, but the older trucks don't have as much draw in the system & the contacts are more robust. The fact that a fuse was blown leads me to believe that there is potential wiring harness damage (melted wires, etc).

 

Identify all your symptoms and clues first.
When you push the brake the truck will shut off, and the park detent solenoid is not working, so first step is your brake switch.. but before you unhook it see what happens if you turn on the hazard lights and also pull the fuse for cruise control. Then the fuse for abs
Write those results down because there is a chance replacing the stop switch wont fix all the problem.

 

very good. noticed cruise does not work.If I turn the truck off in park it stays running as I pull out my key.Hit the brakes and it shuts down completely.let my foot off and it acts as if they key is on and ready to start(full dash indicators). today I put in a board to hold the brake down while i took care of some business ( 1hr) and the battery was dead so something was still drawing. Battery is disconnected now while I make a plan for tomorrow,took the day off.I will start with pettyfogs idea and see if removing fuses helps me identify a clue considering break switch. Also will visually and by smell inspect wire harness. Your help is invaluable,thank-you Gentlemen.

* If I push hard enough on the shift button i here a click under the dash and it releases. how I got to work today.drives normal until shutting off of course.If I turn the key off with my foot on the brake it will shut the down. let my foot off and everything turns back on as if the key is in the most forward advance position. Noticed today though that accessories like radio does not power up UNLESS key is actually in ignition and on...weird stuff. thanks again