NO Oil Pressure While Cranking

I'm ready to fire up the beast and I have been trying to build oil pressure before I start it. I did not take the motor apart (internally) so it seems like it should build pressure since I test drove the motor in the truck before it was pulled. What do you guys think. Yes There is oil in it. When I test drove the truck it had about 40psi. I pulled off the oil filter, there was oil in it but it looked like the brand new oil that i primed the filter with, it didnt have a dirty tint to it at all, and usually when you change ur oil it will still be a little dirty from a little bit of the old oil thats left over in the engine. Thats what scares me if it truly isnt getting any pressure I dont want to start it. I am using my old 94 oil pressur gauge. I have the gray and orange wire cut, and the tan wire is the only wire thats hooked up which is going through the firewall to the gauge. Please help!

It can take like 10-15 sec of cranking without it running to build psi

I have been cranking on it since 11am. I prob have an hour of complete crank time lol. I do it for like 2 minutes straight then stop and let the starter cool off.

Just start it and see what happens. If no oil pressure builds then shut down and ts.

Problem Solved. Fired it up and it has pressure. Guessing the gauge doesnt work while cranking. Now I have leaky cooler lines at the radiator. Going to buy a block off plate rather than new lines. Its not seaping from the threads, but from the end of the line where it goes into the nut thats pressed onto the line. Its just not snug enough. I have them fully cranked down in the radiator, and u can still wiggle the line. BUT IT RUNS!