2002 Ford F-150 truck problem

I have an 02 F-150, when the truck is started and in park the starter will sometimes engaged and grind.. Also I have changed the ignition switch like you told me.. It was effecting my fuel pump, Windows, dome lights, and sometimes when the key was just in the on position the truck would start without me touching the key.. So I did change the ignition switch and it has been fine for about a week and now I came out and was warming up the truck it was sitting here in idle mode in park and all the sudden the starter engaged itself 2 times so I shut the truck off and now I'm sending you this.. What do I do now??? I'm getting so frustrated and I just wanna fix it... Please contact me back, Thank You...