Here's my problem, i got a 99 4d 4x4 this just started today i was sitting in hungry howies parking lot the truck was idleing and the starter kept engaging on its own i shut it off and the starter motor was still running i could hear it then i disconnected the battery for a couple mins hooked batt back up went to start it and i never turned the key over to the start position i only turned the key to where the fuel pump and everything turned on and it started and randomly while driving home the starter kept engaging it was very slushy out today and snowy srry for the book any help will be greatly appreciated

 

visually look at the starter and see if anything is shorting the two big posts on the starter. if not then see if you have 12 volts a the small wire going to the solenoid with the KOEO (position to make the fuel pump and other stuff work). if yes then that small wire is shorted to a Live power feed. If no then replace the starter because the internals of the solenoid are shorting and causing the motor to start unexpectedly

 

Your problem sounds like the same problem from this thread here

https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/starter-engaging-when-shifting-driving-34046/

 

thanks its goin to the shop tomarrow i aint dealing with all that slush **** under there