Mercury 225HP Outboard (2000 EFI) Fuel Problem

I have a 2000 Mercury EFI 225HP outboard with a strange and troublesome problem.
The fuel pump on this engine refuses to turn off, even with key and dead man switch removed. It floods the engine if I don't pull the battery wire off.
I have checked the ignition switch. It checks out.
I have looked for relays. There is none.
I've looked at fuse's shorts ect. None.
I'm now wondering about the ECU's.
There is 2, one for fuel and one for ignition. I hear that there are mini switches in the ECU's that control the power to the fuel pump that in time could get stuck on. I'm wondering if this could be the problem. The ECU's are 400 a pop. Not fun for trouble shooting. When I pull the harness off the top ECU it shuts the pump off.
There are just 2 wire to the pump. Power ground.
So some where there is a relay or micro switch stuck on.
Anyone hear of this problem before?

Can't say I have heard of the problem (but ECU/ECM driven outboards haven't been around long enough to get a good handle on "what is likely" to start going wrong with them after 10, 15, 20 years etc), but you are correct in stating that the ECU controls the power to the electric fuel pump (and that relay or microswitch is internal - with "no user serviceable parts").

Since you have not found a short in any of the harnesses etc and simply unplugging the pump harness stops it from running, there is a good chance the ECU itself is shot. But before I went about swapping it out, even with a used one, I would take the motor in and have it plugged into a DDT at a Merc dealer.

Unfortunately these computer controlled, sensor driven outboards that are supposed to make your life so much easier and save you gas in the process, can no longer be tested or trouble-shot to any great extent in the driveway. In fact, if you suspect a sensor problem and unplug it to check, the ECU will "pretend" it's still connected and feed itself the data it "expects" to see....

Thanks for the thoughts. So it's the ECU on the top that I unplug and the fuel pump turns off. I'll have to try and find
one that I can use to test in the spring. I don't want to be trouble shooting 400.00 each used parts. The Battery kill switch
on the main engine battery has been getting me by last season but it's just a pain in the butt. If that fails I'll drag it over
to the marina and get her hooked up.