When the ignition switch is on, a relay turns the inverter on, the relay lead contains a 20 amp in-line fuse. This relay only turns the inverter on and off and has no other function. The inverter is connected to the battery via a positive wire and a negative wire (not the chassis). The inverter is not grounded to the car at any point and instead, is carefully insulated to ensure that accidental grounding never occurs.
The wire which would normally go to the spark plug is replaced by a wire which is taken to a box containing one pre-war mechanical twin-coil relay or vibrator per cylinder. Each of these wires drives its own dedicated ‘relay’, the current energises the relay coil but the other side of the relay coil is left unconnected. The wiring arrangement is shown in the diagrams below.

It is important that the electrical feed to each plug is fed via one wire to the plug cap and a second wire connecting to a washer clamped under the spark plug. This wiring is repeated for each of the spark plugs. To emphasise this, each spark plug should have two wires running to it, one to the cap and one to the washer clamped between the body of the spark plug and the engine block. The wiring is done with “12-2″ wire which is 2-core solid copper wire American Wire Gauge size 12 which has core diameters of 2.05 mm giving 3.31 sq. mm. per core, the nearest SWG size is 14. The under-plug washer can be made by bending the end of the solid core into a circle of appropriate size and then flattening the wire slightly.
In the relay box, the relays are positioned with a one-inch gap between them. It is important that the physical construction insures that all of the high-voltage connections are fully insulated should anyone open the relay box when the inverter is running. The batteries used are deep-cycle types with high cranking current ratings – this is important because the inverter must stay on when the engine is being started and it will cut out if the starter motor current drain pulls the battery voltage down excessively. The alternator is the stock 95 Amp type and it charges both batteries simultaneously. When the engine is started, the relays are heard clicking until the cylinders fire and after that, no sound can be heard from the relays. It is distinctly possible that the relays take up a fixed, immobile position when the engine is running. The diagram below marked ‘Effective circuit’ is based on that assumption, and it should be stressed that all of the diagrams are only what I understand from the information provided to date.
The engine timing has to be retarded for the car to run off water. This adjustment should be made to the point where the engine runs the best and this is likely to be different for each make of engine. The Chevy ‘Camaro’ engine runs best with the timing retarded by 35 . The spark plug gap used to be 65 thou. but is now set to 80 thou. (0.08”). The plugs used are the cheap ‘Autolite’ (25) copper core type. Using carburettor jets two sizes larger than normal, allows the engine to produce more power and rev higher than tick-over.