I have a 1998 EL Futura and I want to make my Petrol gauge show how much LPG is left in the tank when I switch it over to LPG from Petrol. It has an aftermarket LPG system fitted, which has a switch with 4 led's indicating the LPG level.

I have another 1996 EF Falcon with Factory Fitted LPG, including the factory LPG switch button, which replaces the Central Locking button, and all the other wiring. I would use parts from this to fit to the car i'm doing the modification on.

What would be the best and easiest way to do this? Any ideas appreciated!

i believe ben j has done something along theses lines

Your LPG tank needs the correct resistance fuel gauge mounted on it, which I would presume is already there if the system you have was fitted originally to your car.

Then you use a 5 point relay and hook one input to the petrol tank wire, the other to the LPG tank wire and have it switch to the LPG feed when you select LPG.

Note that switching fuels on the go does not give an immediate response on the fuel tank gauge. The car needs to be turned off then on again for immediate changes to be recognised. The fuel gauge will eventually catch up though.

I have mine set to LPG by default and have installed a switch to select petrol levels by manual intervention.

Cheers
BenJ