What l am thinking is this truck using a Assin propane system if so the early models had to separate small boxes one mounted by the coil and the other one mounted by the air cleaner the one mounted by the coil controlled the spark it used positive out of the box to controll the spark it delayed the spark for approx three seconds the other box controlled the propane it used neg from the coil to open the fuel lock. On the later models they incorporated the spark and fuel into one larger box that was mounted on the frame of the air cleaner it had l believe a plug with six wires attached to it it is possible that the box is bad but that is where the wire is going to it. When cranking it see the neg signal and starts the flow of gas if not this propane converter is a positive displacement meaning it gets fuel as soon as the key is on.with out the box it would get fuel with the key and there is a chance of a fire without it it will not open the lock untill it sees the engine cranking.hope l was of help.