Spectacular growth on the battery terminal! This is on the link cable on the -ve battery post.
Switch fitted to the heelboard, take account of the strengthening ribs and position of the cable before marking and cutting. Fitting the switch from the back of the panel would have resulted in a simpler hole and better sealing.
Switch with cables and boots fitted.
Batteries cleaned up and reinstalled. My battery cables are all black so I have wound some red plastic insulation around the ends of both the main cable and the +ve end of the link cable.
Finished switch. Let's hope I never need to use it 'in anger', although when garaged I shall always turn it off.