My 24 Valve did about 18 psi in full bypass engine off, about 15psi cruising and around 12 psi both feet flat on the floor with an aftermarket stock style replacement pump. The factory spec was 5-7 psi IIRC.

I would bypass the original lift pump as it will just be a restriction. 18 psi is pretty much stock spec for a 12v from what I read and the more you step on it the less it will be.

Just use an oil pressure gauge if you need something with a light in it. Diesel fuel is oil technically. Lol.

Kevin