Shurflo 4008 RV Revolution by pass pump

going on memory

the very front wire is power
the wire behind that goes back to positive on the rear of the motor

On the pressure switch does the front connection go to the motor or power? Brick

is it pumping water ?
it will run backwards if the wires are reverse and will not build pressure and shut off

if its pumping water, start at the pump head and remove the wires plugged into the pressure switch, switch is defective or wired wrong, or adjusted wrong

Your 4008 model has a Pressure Switch that turns pump ON/OFF based on discharge line pressure
Starts when pressure is 35 psi (or lower) and should shut off when pressure reaches 55 psi

And an internal 'bypass' that opens/closes based on pump discharge pressure.
Starts opening at 40 psi and is full open at 62 psi


Pressure switch adjustment is done via a small allen head screw. Located to left of 'square block' where RED wire plugs in)

Bypass adjustments are done via small allen head screw BELOW the pressure switch adjustment screw

Following is from an installation sheet

About The By-Pass
NOTE: By-pass adjustment should be performed by professional technicians with proper gauges and equipment.

The by-pass is a spring loaded diaphragm that opens up allowing water from the discharge side back to the inlet side.
The by-pass is set to begin opening at about 40 psi and creating full by-pass at about 62 psi (for 55 psi models), lower pressure pumps will vary depending on the by-pass and pressure switch settings.

If the switch or by-pass are adjusted too much, the by-pass and switch shut-off can overlap and THE PUMP WILL NOT SHUT OFF.

Screwing the pressure switch screw in clockwise will raise the shut-off pressure.
Unscrewing the pressure switch screw counterclockwise will lower the pump shut-off pressure.

Screwing the by-pass screw in will raise the pressure at which the by-pass starts and raise the full by-pass pressure.
Unscrewing the by-pass screw counterclockwise will lower the pressure at which by-pass starts and lower the full by-pass pressure.

WARNING: If full by-pass is reached before the shut-off setting, the pump will not shut off.
Full by-pass pressure setting should be at least 5 psi higher than pump shut off pressure.

Good Luck! Always make small incremental adjustments then test results

Possibly a defective pump. My old one last fall wouldn't always shut off so I replaced it with a new one and it fixed the problem.