Battery Cutoff Switch

Porsche 928 Electrics

Electrical information & supplies for late model 928s

Battery Cut-Off Switch:

This is a simple but very convenient addition - especially since the 928's battery is buried below the carpet, cover & spare tire. On the older cars the ground strap form the battery to the chassis behind the rear tool panel was fairly easily removable with a wing bolt attachment. On the later cars this just used a regular bolt and takes some time/effort to remove.

I decided to fit a heavy duty battery switch to this ground point location so I could easily and quickly connect and and disconnect the battery. Since I do a lot of work on my car this was convenient for me. It also helpful as a security measure, to prevent battery drain during long periods of no-use and as a way to isolate the battery from the car for rapid charging. In the end a very handy thing!

The idea is simple but the fabrication is complicated by the limited space available and the need for heavy duty connections & switching - this needs to handle starting currents of ~500A. A Note - any battery switch should never be turned off when the car is running.. it won't stop the car - but will compromise the voltage regulation which can cause very expensive damage...

Rear & side views of the cut-off switch with ground strap attached & ground bolt in position

Final install location - barely room here but location is fixed by the ground point Final cut-off handle view

In the final version I cut the switch handle off flush and cut a screwdriver slot into the end... easier to fit behind the tool panel and is still easy enough to switch. Additional handles are available inexpensively if you need to frequently switch on & off.