Before you start looking at this - I cannot stress how dangerous it can be mucking about with the fuel system of any petrol or LPG car. Just cos it's LPG - and you can see all the bits and the wires are all there to play with does not make it any safer. If you don't know what you are doing - then leave it to a specialist.
You have been warned.
OK - here we go - I'll add what info I can...
I'm not sure what gas system you are using. There are three main types.
Mechanical - where a mechanical regulator governs the amount of LPG to add to the incoming air into the engine. This mechanical regulator will have a simple solenoid on it to switch on and off the LPG ( and by law, another one in the LPG supply as a backup)- In these systems, on an injected car, there will be a box of electronics (or two on a V8 - one for each bank) to switch off the injectors. These boxes fool the engine management into thinking that all the injectors are fine and dandy when running on gas. Nice and simple. The solenoids of the regulator and the valve should be connected together (and to the solenoid in the tank) , and connected to the green wire. Some installations use the yellow wire to switch off the fuel pump - leave this disconnected if you have the injector emulators installed.
Single Point System - this uses an electronic ECU to control the fuel - there will be a solenoid valve in between the LPG regulator and the air intake. The wire colour is the same - green goes to the LPG solenoids - but this is more complex - best to take it to someone who know this stuff.
Multipoint system - this is similar to the above, but has one solenoid valve pre cylinder - as with the single point - this is pretty specialist, as it's a laptop out time.
I am concerned that you say that the LPG connection goes before the flapper valve - this is unusual - it is usually as close to the throttle as possible...
If you are in any doubt, take it to your local LPG fitter, and ask them for an opinion. The worst they can say is no....
I reccomend HKL gaspower in Brum... Very Helpful - ask for Steve the fitter...
If you want to delve further - lease ask - but heed my warning - it can go wrong in a big way...
Mike.
Under the bonn