My co-workers truck (99 F150 5.4) starts just fine in the morning. If he lets it sit for a half hour after the initial start, turns the key, nothing happens. He hears clicking under the dash. If he waits 2 hours or more, the truck will start. If he swaps the battery, it will start, no problem, but he can't jump start the truck. Both batteries are new and he's cleaned the battery cables both on the battery and on the frame. What could it possibly be? I'm thinking the starter relay or the ignition module?