Pictures of what you have would be useful.

Depending on the filter/ fittings/ cannister you have there may not be any restriction in the bypass oil filter. A restriction is needed so as to not rob the engine of too much oil pressure.

If there is no restriction the gauge won't register any pressure, same as it would not register if connected straight to the crankcase, or in the oil return line, or anywhere after the restricted fitting if there is one.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-