Onan 10K generator for home use-removed from the rig.

Here's a link to a YouTube video of a Onan Quiet Diesel 10kw generator:
https://www.youtube.com/watch?v=p3nx7OIExHI

Apparently all you need is a battery and fuel supply. The remote start panel should not be needed.

The Onans use a bunch of latching relays. You will need wiring diagrams from ONAN not Cummins. I take it this is a diesel.

Start Run circuit
Safety shutdown circuit
Both are needed.
Onan is famous for using 3 colors of wiring and ID numbers on the wire.

The plastic rings around wires are current sensors. Do not remove. Anything with a plug and socket should be unplugged and doused with Caig DeOxit D100 then replugged.

You need a ganged 240 breaker near the machine.

The generator must be enclosed with ventilation. It cannot survive getting wet.
Long term storage plug the exhaust with a rag. I strongly recommend a RAcor fuel water filter. If the unit has glow plugs I also recommend a push button over ride if temps approach 0°F.

Keep the unit high enough off the ground to make oil changes easy.

To get the generator running, your friend will need a 12V battery and an AC powered battery charger as the generator most likely doesn't have a battery charge circuit built in. (It's an option on at least some of the Onan RV generators, rarely fitted.) Probably it's unnecessary to worry about the other wires for the inside remote control and hour counter and pilot light for basic operation; the start and stop switch on the generator I think should work just fine with them left unconnected. Of course, having a remote panel would probably be more convenient.

I'd think an old but not completely dead car battery, or a not old riding lawn mower battery, would suffice for starting the generator.

A generator interlock kit for his main circuit breaker box costs less, is easier to install and much more flexible.

This really has nothing to do with getting the generator running but it will be the next step.

The 120/240 output can be wired onto a standard range receptacle or wired into a transfer panel in the house. Transfer panels are available at many big box hardware stores.
On like this
Transfer panel