lpg wiring help please

hi chaps i have a rr classic which i have fitted with lpg from another rrc. It worked fine before removal but now i cant find the trigger wires. The only difference is it was a 3.5 and now a 3.9. I have not yet plummed in the gas cos i want to get the electrics sorted first.

She starts and runs on petrol fine. The gas switch displays how much gas there is but when you switch onto gas the light used to flash then once you rev it up you got a click from the tank the light stayed lit and everything was fine.

Now when you switch over the light is green all the time but it does not switch.

I did not cut any wires when i removed it and they have all gone back in the same place. Whats missing.

Does anybody have a wiring diagram as i have looked at the gas loom and somebody has bodged it. some wires have been cut.

Also there has been a wire added in the loom. stick 12v on it and it works but it works all the time and doesn't stop with the engine.

Can anybody tell me which bit actually works out that the engine is running and switches fuel.

Its a range rover classic with multipoint inj and the system is landi renzo.
Any help much appreciated. Sorry for being so long winded

Before you say it is wired to the coil but the wire doesn't seem to do anything

No worries its sorted. I just had a play and despite wiring loom being tampered with it does work. Appears that the tach is taken from alternator rather than coil. Swapped wires and he presto.