The circuit breaker, when operated, must isolate all electrical circuits with the exception of those that operate fire extinguishers.

Types of system.
These can be cable operated or electronic.

Cable operated
The cable system suffers the age old problem of the cables seizing up. You must keep these lubricated so that they operate freely.

Electronic unit.
This comprises a contact breaker box and a external operating button. There is also a reset button.

Trigger switch location.
The triggering system for the circuit breaker on saloons should be situated at the lower part of the windscreen  mounting, preferably on the driver’s side or below the rear window.
On Open Cars it should be situated on the lower main hoop of the Roll-over Bar on the driver’s side or at the lower part of the windscreen mounting (as above). Alternatively on cars of periods A to F the mounting point may be mounted approximately vertically below the line of the scuttle on the driver’s side.
The location must be identified by a Red Spark on a White-edged Blue triangle (12cm base), and the ‘On’ and ‘Off’ positions clearly marked.