Where are you guys tying in for your water pressure gauges. I have a Livorsi mechanical water pressure gauge, its on a gen 6 502 mpi, and curious where people were connecting the tube to the motor for a good reading?

Ayuh,... Tappin' into the T-stat housin', where the temp sender is, will give ya Block pressure, which is the important point to Me,...

I put mine in place of one of the block drains...

They're tapped into the T-stat housing for the 6.2 MX Mercs in my boat so I guess it should work for your 502 too. I have tubes installed as well to back up the SmartCraft electric with manual gauges.There are plugs on the right hand side of the T-stat housing where to install sensor or mechanical fittings.

Yea I don't have a factory t stat housing as I have a crossover kit with bypass. I am going to take a better look around, as someone told me there should be a plug in the intake right there I could use. I am not getting much reading at all out of the drain hole in the block, but I am flowing plenty of water

If you are running it on a hose, you won't see more than a few psi. Might see 5 psi with reving it.
Readings from the block or intake should be the same.

Block drains clog up with junk and won't read anything on the gauge. T stat housing or intake is a much better place

Yes, they will clog. That's where mine is connected and it fills with sand and junk.

Since I have to remove the hose to drain that side of the block anyway, I break the connection to the gauge under the dash and blow it out with an air hose as part of my winterizing process.

Mine are the block drains and never a problem. I don't beach or shallow water, so never an issue.
On a different thought process, when your block drain connected press gauge do stop working do to sand or whatever, you know it's time to flush your block.

Now the question that begs is what pressure do you want? Flow is more important of course and is often inverse of pressure (such as if you had an outlet obstruction yielding very high pressure, low flow and overheat) A fire hose has no pressure at the end but great flow. If you plug the fire hose then the pressure at the end will go high as flow goes to zero. Not as simple as high pressure good, low bad. Flow. An interesting puzzle.