I believe that is a low idle solenoid if it is round and has 4 screws
The small one is the High rpm solenoid
The voltage comes from small engine controller
Or secm the secm sends 4.6- 4.8 volts to solenoid. When key is turned on
It should engage for a second then shut off
That small amount of time fills the cavity with lp for starting after the start it opens and lets lp into mixer and the rpm sensor sends signal to secm that it is running and keeps it open
If it is dying I would check 1- lock off solenoid
2- rpm sensor 3 - vaporizer
The solenoid will show voltage only if engine rpm is reading