Trying to set timming on my 1994 gmc jimmy s-15 4.3 vortec. It calls out to unplug the timming conector? I have no idea what the book is refering to. I unpluged the four wire connector on the distributor but the motor wouldn't turn over.????

The switch that you mention its located under the carpet, on the firewall on the pasenger side. You have to disconnect it before the timming its adjusted, the #1 cylinder its front pasenger side