Dear Shahid,
I am assuming you are using Landi Renzo 094 CNG system.
Since you have already get the switch and wiring harness changed but problem still there. you need to check the following
- Red wire of switch must be connected with Ignition key.
- Black wire must be connected with ground (better in battery negative terminal)
- The most important (brown wire) must be connected negative on coil or make turns (not more then 3) to high voltage of coil wire.
you can also increase the prime timing of switch, if you have 3 way switch there is a prime timing adjuster on back side OR if you have push button switch you can reprogram it.
for other support you can directly write me " murtaza@landirenzo.com.pk"
Murtaza