Man needs bling!!!! You have to point it out to people, even down in the bilge... LOL... Just kidding. I don't know if I would do it again after all the stories I've heard. I have a friend that has one on his boat and he has talked to a big name place out in CA and they don't believe there is enough flow with the Hardin pump. I don't know if any of it is true or not. All I know is, I never had an alarm with the old OEM pump on it, but I have had several since I changed over to the SS pump. I am going to go back old school and revive my OEM pump and hopefully, this issue will go away. If between putting the old pump back on and cleaning the outdrive oil reservoir, I still have the problem, then I will really start worrying.

What exactly you mean by re engineering the stock pump?

On my 496 pumps, I deleted the quick drain back plate with a stock plastic ones with the replaceable wear plate. The quick drain pumps were a nice idea but my actuators eventually stop working and weren't something I used anyway. I always do a full antifreeze winterization on the fresh water side. Probably saved about 10 pounds too...those brass drain backplates were HEAVY!

I have deja vu all over again. Did you buy a complete pump or did you just back half it? Are both wear plates in there? This pump is just like the merc. unit except that it’s not a plastic time bomb. I would go back through the installation and recheck everything. Maybe flush any lost impeller bits out of the cooler intake hose. Something very simple has been missed in every one of these “Hardin Pump” posts. Good luck man and I hope you don’t put that plastic POS back on your boat.

So, true!! Yogi Berra quote. One of my faves is "If you see a fork in the road, take it." But I digress. Complete pump. I really won't know until I get it scanned and the new water pressure gauge installed. It seems that it pumps enough, but who knows. As stated, engine temp is perfect. Risers are not overly warm using the hand (forgot my infrared temp gun last time out). Looks like plenty of water out the exhaust. The pump was originally installed straight from Hardin. Strange, but that's when the BS started. New impeller this year. Not near enough hours, but time got me. Even at that, the impeller was perfect other than set to some extent. As simple as it was, about the only thing to go wrong is failure to install both plates or installing the impeller the wrong way. I triple checked it and then checked it again before buttoning it up.
As Griff and others said, it could be the drive oil reservoir sensor also. So, that will be my first little project before it gets scanned. Clean it out and re-install it. If that doesn't correct the problem, then it will get scanned. If it turns out to be a pump flow issue, then sad to say, but it'll be bye-bye time.

I have used several of the Hardin pumps without issue. As Griff said. there isn't an alarm on a 502 for water pressure, just over temp. You stated that your temp is perfect. I seriously doubt that the new pump is causing your alarm.

Before you start changing parts, figure out which sensor is setting off the alarm.

All the wires for the alarm system are tan and blue. The alarm sensors are separate from the gauge sensors. The only sensors are for low drive lube, low oil pressure and high water temp.
Pull the wire off each alarm sensor one at a time and see if the alarm quits. If it does not quit, then one of the tan and blue wires is grounding out somewhere. I had it happen once and a spliced wire had come apart and the wire was touching my intake manifold and grounding out. This completes the circuit and sets off the alarm.

I will check first. Thanks

1996 7.4LX MPI's here with Harden Impeller housings and Merc. impellers for several years without issue. Didn't see a need to go full pump so still have 1 25 yr. old OE Merc. unit and an aftermarket (not hardin) on the other engine.

I have been running the Stainless housing for years and it works great. I'm pushing 700hp and no cooling issues at all even at extended wide open. I did go through it and ported it to improve flow and reduce turbulence. I have found my impellers last way longer with the stainless housing. I did modify my exhaust to increase flow. I also ported the water inlets on my Bravo drive and filled in the top 2 holes as my drive height is pretty high so I don't suck air at high speed.