On our Axis there is a switch on the dash labelled something like "emergency start" or something...sigh don't remember the exact text on it. When held down it shorts the house battery together with the chassis battery allowing the house battery to start the V-10 or the chassis battery to start the generator.
I know some Thor motorcoaches don't have it, however (as people have indicated that was not present on their coach on the forum here).
Update: Ah here is a pic:
To the right of the lit generator switch is "Emer Start".
Thor Forums
