Is there injectors positive lead fuse or relay?

Dears, it's me and my scrap of car again.

Little introduction to the question: The original car type is 2.0 but engine is replaced with some Mondeo or Focus engine Zetec 1.8.
There is some "professional" LPG system installed on the car.
It is (I think first generation) mono injection system, only with evaporator and mixer mounted into a resonator placed on throttle body. Inside the car there is only a simple switch 1-0-2 which is manually controlled, on 1 the fuel pump runs, and on 2 fuel pump stops and electromagnetic valve on LPG evaporator opens.
I noticed (a long time ago) that I was always missing gas (petrol) even if I drive only on LPG.
Today I made a test with LED test light, and noticed that when the engine runs on LPG only fuel pump stops but injectors are still pulsing (that as I know mean that every time when injector opens, a little amount of fuel is sucked by the strong engine vacuum).

So, the main question (before go and waste money to local "experts" is to try and solve something by myself.
Injectors are with continuous + from battery and pulsating - from ECU/PCM. Is there (in the middle of + lead) some injectors relay or fuse, where can the stopping be done somehow (by additional wiring)?

Thanks a lot.