The truck will start to turn over by it self. Like someone is bumping the key. Only happens when the key is on the acc postion. It takes it like around 15 mins or a little less. We're should I start to look for a short if that is the problem

 

a faulty ignition switch.
with the key in accessory, check for voltage coming out of the ignition switch to the wires that feed the starter solenoid.