Dave wrote;
>>I installed a shurpower 1315 isolator. It is so simple, I don't know how I
>>messed it up.
>>I hooked up main battery + to one terminal, Aux batter + to the other
>>terminal.  I left the 3 little switch prongs alone, as I don't need it
>>manually switchable, just want it to intelligently charge the aux battery.

Dave,
Step 7 on the instruction sheet says to connect a 14 gauge wire from the chassis ground to the Separator ground.  (this is one of the three prongs you left alone).
When I hooked mine up I ran a short wire from the ground connection to one of the mounting screws I used to hold the separator to the vans body.
George
'85 Westfalia (with two batteries and a Sure Power 1315 Separator)