Need help 2000 rexhall aerbus

Is the battery charged?
If yes, you can jumper the two large posts on the battery disconnect to energize system.
If yes, have you checked the control fuse?
If battery is not charged, try using the auxilary start button at the same time as battery disconnect enrgize button with engine running.

Is this your first RV is the salesmans switch usual by the door on??? Do the batteries test over 12 volts?? Can you plug into 120 volt power?? If you can get 120 volt power you should be able to get 12volt inside and the the batteries should start charging. Can you start the motorhome? if so start the motorhome us the booster switch to start the generator the generator will power the charger to give you lights and charge the batteries.

Yes they are charged just bought it 2 days ago dealership said it needed new battery. Installed new batterys had power 1st night went out next morning now power to inside can start rv but can't get any lights to work

Yes 1st rv the switch by the door worked the first day now nothing for the coach side the chassis side stays red even when you push it off

Did you clean and tighten the battery terminals? And, check the voltage of the battery(s)?

Always do the basics and make sure the batteries are charged and properly connected before you start to diagnose the problems.

Yes terminals are brand new clean and tight. The day before I could disconnect it at the switch now it will not connect when you push the switch is there a way to jump the switch from the wires in the back of the switch

Switch no,(not easily)can be done easily on disconnect relay by jumpering large terminals

How do I do it on the relay and where would I find it

Maybe you should contact the dealer and explain the problems you are having. Changes are that they can help you with the problem. It may of had this problem when you acquired it, and they may help you out. It is very hard to help someone with a 16 year old MH, that they have just gotten, on a forum, especially if you are not familiar with it.
Good luck and let know what happens.

Gas powered rigs normally have it in the battery control center under the dash.
Some have them adjacent to the batteries under the step.
Use a heavy piece of wire around a #6 or 8 to jumper large terminals. I would verify the fuse in the control center or on relay is good first.