re: What do diesel techs make?

Depends on his skill level & experience level.

He is probably not gonna start out making OT type money but will have to work his way up from the bottom.

Does he want to work on light duty vehicles(Ford Super Duties, GM, Dodge Ram, Nissan Trucks...)? Find a Ford, GM, Dodge, Nissan dealership...

What about heavy trucks? Sterling, Freightliner, Kenworth...try those dealerships.

Heavy machinery, ie bulldozers, cranes, tractors. Try Cat, John Deere, Kubota, Komatso...try those dealerships.

Main thing is to get some real-life, hands on experience. A man won't get too much of that at a school.
He will probably have to 'struggle' a couple of years.