You have it wrong!. That wire provides power to the ISC, when the Injector Power is cut off while on LPG. Normally the ISC is powered from the same source as the injectors.

Otherwise your ISC wouldnt work when you on LPG.

Nigel

yes check that the isc has power to it at all times (on pet and lpg)and that u have continuity with the ecu on the other wire...