What Alex said.  You have an open ground on the house battery.  As soon as
you connect a load to it the positive terminal floats at chassis ground
level, and the negative battery terminal is now -12V to chassis.

Yrs,
d

On Fri, Jul 12, 2019 at 2:03 PM David Boan <dboan@outlook.com> wrote:

> I am working on correcting a short in my accessory wiring, and while
> making progress I have hit a plateau.  I thought someone might have
> experienced this and could save me much time searching ...
>
>