Volvo Air Horn not working

2020 Volvo VNL 760 air horn located above batteries, under the cab. Don't confuse it with city horn.

- If air is coming from the hose - replace plastic horn.

- If no air coming to the hose - proceed to the next steps (electrical signal is not pushing air through solenoid for some reasons).

Four solenoids are located under the center of the truck on a cross member, facing back.

- if 12V is coming to the solenoid - replace left solenoid ($100 part and 40 mins work).

- if 12V is not coming to solenoid - proceed to the next steps (wire issue somewhere above).