I have a 1981 Blazer 4x4. It has a 350 with 350 turbo tranny. I was given the truck had a few issues got it running. One day I hooked up the brush guard lights that were unhooked they are wired straight to the battery. Dont really know if this is part of issue or not. What is happening with the engine is it is hard to start, you crank and crank it and it wont start, but sometimes you get lucky and it fires up. If you can keep it running. When it gets warm it will run by itself. But engine would die if you touched brake pedal. I unhooked brake light switch by pedal and this stopped , but know engine dies if you put it in gear. And when it dies it goes back to not wanting to start. And ignition works off and on, may crank several times turning motor and then goes to nothing like your not turning the key, just turns on dash lights. Checked engine timing and was ok, new plugs and wires. New carburator, racking my brain on whats going on. Any ideas of whats going on will be helpful.

 

It sounds like an electrical problem.
Was there a lot of aftermarket wiring on the truck, does the wiring appear to be a mess under the hood or dash?

 

yes it has an old alarm system on . and the wiring under dash is a rats nest. The only thing that is wierd it was running fine until I messed with the brush gaurd lights. When I first hooked them up the didnt work ground connection on them was all rusty. I cleaned connection hooked them back up to battery they blew inline fuse the next day. Shortly after this started I have disconnected all wires for lights.

 

Is it possible you blew out a ground strap/connection or a fusable link somewhere? Poor ground can cause all sorts of weird stuff..