The fuel shut-off valve was illustrated in an old copy of TR Action magazine of the TR Register; it requires 12 volts to operate. I have added a safety relay which was recommended by the seller of the valve Tinley Tech Limited. 01767676181. www.tinleytech.co.uk
I have been assured by the manufacturer that the relay works with positive earth as long as the polarity of the connections are observed. I have not tried this on a positive earth system. Both the shut off valve and the relay are in insulated packaging.
The valve should be sited in a discrete position in the fuel line before the fuel pump in a position which gives access to the manual override lever. There is a direction of flow indication. Use connecting pipe which is compatible with modern fuel.
Because the valve could overheat when operating if no fuel flows, (if the ignition is on without the engine running) a relay which is triggered by pulses from the distributor side of the coil is used. A hidden switch can be inserted into the valve feed for additional security.