Sea Ray

No, compressor fills tank. Gauge is stuck at 100 psi so I’ll replace it first. Then I’ll have to find the solenoid?

Yes, get a working gauge.

The compressor system has several parts that must all work properly. There is the pump. The unloader / check valve ensures pump air enters the tank and doesn't go backwards when shut down, it also depressurizes the pump when shut down so the pump may start w/o working against a pressurized tank. There is also a pressure sensing switch, probably fixed settings, shutting off at a high pressure, such as 125 psi and turning on at a low pressure, such as 90 psi.

In a system like that there is a solenoid valve (or a manual lever valve) that toggles pressurized air to the horns. The optimum valve placement is close to the horns, so sharp action is possible and so the off sound doesn't bleed down.

Fixed. New pressure gauge, solenoid valve in center of roof cleaned out and diaphragm in air horn cleaned.

Thanks for the update.

What corrected the problem requiring manually flipping the lever on the compressor to have it automatically stop?

Junk in solenoid valve let it leak by.