Start with the easy stuff first.
1. Make sure he is in neutral AND the EBrake is SET.
2. Batteries, (two) are in good condition and fully charged.
3. Battery switch is ON. He has two switches, one in the battery bay for the house batteries and one in the engine bay near the batteries. Make sure they are on.
4. Turn key to ON position. Does he have power? I know you said he has dash lights, anything else? such as radio etc.
5. With the key in the ON position, remove the panel cover from the rear run bay and press the start button there.
Try these five steps and let us know how he made out.....Dennis