Hi Aaroncast

The 3 Ohm shunt resistor is no problem, I've had it connected since I wired the car 3 yrs ago.

Perhaps the book I read was a bit old and a little out of date?

Everything at the same protential is the outcome, so being at Gnd or +12V is relative. It could be wired both ways.

The reason I asked was that I could not see a benefit of switching the neg side.