The factory harness has separate ignition switch wires for crank and run. On my FI install I simply spliced these together in the engine compartment to trigger the computer. It is a big splice because the ignition box and fuel pump relay need the same signal.
I'd seriously advise only using this splice to control a relay that supplies the 12V to the FiTech unit.
On my setup main power to the FI computer comes from a heavy wire right from the fender relay. The ignition switch feed I described runs a relay inside the control box to switch it on... and carries very little current. Agree the ignition switched lines I used are not suitable for main power supply.
