Mike you can not hook the wire for starter at key switch to coil because it will back feed after it starts through the run terminal and start cranking the truck when it is running. You could get the correct switch from the dealer and install. To do what you want to do you could add wire at s post at starter but you would have to install a diode in line from s post to coil to stop it from back feeding when running. You could just take that wire out of the circuit and just wire to ballast and see if it starts good if so don't worry about it.hope l was of help.
Thank you Scott. I did find a wiring schematic that shows pin 1 thru 4 on ignition switch. Pin 4 going directly to positive of coil. I wasn't sure if it was only powered while cranking. That being said, I appreciate the help and I think you are right. Also, someone replaced the ignition switch recently with a universal 4 pin switch, probably why it has power all the time. Could I hook the coil wire up at the ignition switch on the same terminal that goes to the starter for cranking?
I will try to answer this question what l remember was Yale used a four wire key switch plug in connecter the key switch was marked one to four the first was battery the second terminal was ignition to coil the third terminal was start for cranking and the fourth terminal was its own circuit that only got current in the crank position so it would apply battery voltage to the coil before the ballast resistor and then the run position would control the ballast resistor. /hope this answered your question