[A1971Blazer]

more than likely the switch is bad since it stays running if you're barely off the start position...or the connector on the back is bad....or a break in that circuit...
you can pull the connector off the back of the switch and take a look at it.....
to remove the switch...you need to turn it to acc mode.....push in the little hole with a paper clip...and the cylinder will come out.....
then unscrew the bezel off the front...that will let it come out...