If he lost the ground to the starter, he should still be able to turn the key to the ACC position and have the electronics in the cabin turn on (I think). Fuses should always be the first thing to check though.
Check the ignition lock cylinder. There is a little piece on the inside of the cylinder that moves the ignition switch actuators inside of the column. If that piece breaks (not uncommon), the truck will recognize the key is in the ignition, but won't have any idea if you have turned the key or not. It is very easy to check to see if it broke. Look under the the column at the piece of plastic between the wheel and the dash. There will be 4 holes. 3 of them have screw to hold the upper and lower plastic covers together. The other one is the lock cylinder release. Get something long and skinny to put in that hole, and apply slight pressure (just enough to press in a tiny button). Put the key in the ignition, and turn it slightly until you feel the lock cylinder release press in. Once is does, you can pull the cylinder out with the key still in it. It should look like this
https://images-na.ssl-images-amazon.com/images/I/41vvnDJQ8+L.jpg. The part that breaks off is that tab looking thing on the left side. If it did break, you will need to replace the cylinder (either with new keys if you don't have PATS, or re-key the lock to match your current keys), and grab the broken end piece out of the column.
If it isn't that, you should just go down the line to find your problem. You can remove the plastic, then metal lower dash covers by your knees with 7 mm and 8 mm sockets. Find the ignition switch, as Harua216 mentioned, and unscrew it from the mounting point with 2 T30 torx screws. Once it is down, you will see a metal peg that normally sits up in the column, and is connected to the ignition switch actuators. Move that peg backwards and forwards (with the key in the ignition) to see if you can get the the truck into the ACC, Run, and Start positions. If nothing happens when you move the ignition switch peg to different positions, it could need replacing ($15).
If the ignition switch goes through each position fine, and the ignition lock cylinder was in good shape, you probably have broken/disconnected actuators inside the column. They just connect the lock cylinder to the switch through inside of the column. If they come apart or break, there will be nothing to push and pull the switch peg when you turn they key back and forth. You would also notice no movement in the lower actuator (where the peg fits into) when you turn the key.
