Wizard I believe that is all dependant on the isolator used. Some are dual sensing and others are not. As you've described I think it would require a dual sensing isolator to feed from the Aux to the starter? Also another point to consider is if the isolator requires 'ignition' to be live for it to work, I have a piranha dbe180s and it does require ignition to create the link, although if I was to install a permanent solar panel I would look at putting the 'ignition' feed wire to the aux battery and having the isolator on full time and running the solar through the main battery (as I believe the DBE180s is not dual sensing). Would this work cuppa??