Wanted to make a pump pressure tester which is available all the time with just a hit of a button. I do not see how you could get an accurate measurement of pump output with the nozzle hooked up? So I was planning on putting a tee in the line and connect an alcohol safe transducer and then getting a NO (Normally Open) solenoid and connect it after the tee on the nozzle side so when you were testing the pump the nozzle would be blocked off. Finding an electric gauge that measures over 100 psi has proven difficult. But I do not see why you could not just use a simple voltmeter https://www.amazon.com/DROK-Digital-Voltmeter-Voltage-Monitor/dp/B00H8KNQUQ/ or an actual car gauge if it measures that low. 4.5v on the transducer means it is registering 150psi. Voltage value degrades linearly with pressure so you could make a reasonable assumption of the condition of your pump. Could splice in a momentary rocker switch on the PWM power line to the pump so you could give the pump a full 12v for testing. Only issue I potentially see is loss of flow going through the solenoid - a 1/8" solenoid is smaller than 1/8" at the value. But maybe getting a 1/4" solenoid would solve that. Off base with anything here?