M H will not start

Yes there is a relay and you can hear it click when you push the battery switch.
First put a battery charger on the rig and see if maybe the battery may be low and cannot make the switch work.
There should also be a way to get the house batteries to help start the rig.

has he tried the dash switch to link the house and chassis batteries?

Make sure that both battery sets are connected, and the salesman switch is on.

Sounds like a starter solenoid to me.
check for 24 volts at the starter, when the key is in the start position.

Does it crank? and not start?
or
does it not crank at all?

sch911 wrote:
Make sure that both battery sets are connected, and the salesman switch is on.

If it were off, nothing will work. his lights come on.

might be something as simple as a loose or corroded battery terminal or cable end. pull the connectors on the battery and clean them and the cable connectors well. if that's not the problem be sure the starting battery is good by checking each cell with a hydrometer. if still a problem use a DC volt meter and start tracing power upstream between the battery==>solenoid==>starter making sure 13.8 volts is present at each point.

In the back run box there is a switch for starting it from back there.

Tom/Barb wrote:
Sounds like a starter solenoid to me.
check for 24 volts at the starter, when the key is in the start position.

Does it crank? and not start?
or
does it not crank at all?

Suspect his coach is wired 12 VDC, not 24 VDC.

Totally agree with the rest.

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

Also check for a bad ground on the chassis battery cable. I had that happen on a motorhome.