Gas To Butane Conversion Wiring Problem.

My friend has a 1998 Isuzu Rodeo that he has istalled a butane conversion kit. The conversion came with an auto switch that works like this. Once you start the rodeo, and reach a 2000RPM level, the conversion electronics would automaticlly switch over to butane. The problem is the impulse signal used from the rodeo was not holding the switchover and the rodeo would switch back over to gasoline. What wire, or signal sould he be using to provide the impulse signal? Thanks