Moving Generator Starting Cable

[dandick66]

My 2012 Diplomat generator uses the house batteries for starting.  This is a poor design as the generator struggles to start from them.  I’ve seen posts where users add a separate starting battery and isolator up front at the generator.  I was looking into this when I thought I’d look at the possibility of moving the starting cable from the house batteries to the chassis batteries.  
                                                   
I found where the generator cable is connected to the house battery bus and found an empty connection on the chassis bus.  I can make a jumper/extension for the cable and get it moved, but I discovered something with the power that I don’t understand.  When I turn the house or chassis disconnect switches off, I still read voltage on both buses.  However, if I turn both disconnects off, I only get voltage on the respective buses when I turn the chassis or house switch on.  If I turn both switches on, after about 30 seconds I hear the Big Boy energize and then I get the same symptoms - if I turn either switch off, there is still voltage on the buses.  I thought the Big about was an isolator and would only pass power when charging, or when you push the battery boost switch.