If you have both an Aux Battery switch and an Aux Start switch, there will be two solenoids near your house battery. The Aux Start solenoid will connect between the house and chassis batteries and the Aux Battery solenoid will connect between the house battery and house circuitry. Mine connects to terminal post with a couple of cables leading from it to the house circuitry.
Whether or not you have both should confirm whether or not you have both switches. If you do, you may be able to trace the smaller wire from the solenoid to the switch.
2002 Itasca Suncruiser 35U