Note: If you have the newer MFI display found on Virage and Genesis watercraft the reset method can be found in this thread.
This method is experimental (but seems to be working on each MFD display I have tried it with, so far). There are several unanswered questions regarding what exactly the various reset sequences (also known as CALibrate) actually do.
It has been documented for some time now how to 'reset' the MFD display to 'correct' an inaccurate voltage reading (LoPWR) on the MFD display. In my case I often ended up with a working but UNcalibrated voltage reading. For me, the result was typically that the MFD reads 1 to 2 volts HIGHER than the actual battery voltage. Until recently I had not done extensive experiments to determine why this was, or how to get a more accurate voltage reading on the display.
In the attached videos, the actual battery supply voltage was about 0.75 volts lower than the 13.9 that is displayed. Actual was just under 13.2 volts, measured with a Fluke 23 III.

Update: See this post. The MFD volt reading will only be accurate if the actual battery voltage is exactly 14.00 volts during the calibration.
If the battery voltage during calibration is less than 14.00 volts, the display will read high by the difference. In the example above, the actual voltage was 13.2 volts so the display read high by; 14.0 - 13.2=0.8 volts.
If the battery voltage is above 14.00 volts during calibration (such as when the engine is running) then the resulting voltage display will read LOW by the difference. If the charging system was providing 14.5 volts during calibration, the MFD will afterwards read 14.0 - 14.5 = - 0.5 volts (so the readings on the MFD would show 0.5 volts LESS THAN the actual voltage).
Note: This was initially tested on the oval MFD that I had on hand, from a 1997 Polaris Hurricane watercraft (model 3280224).
I have since successfully reset the Engine Hour counter and calibrated the voltage display on the following MFD part numbers;
3280252
3280202
3280147 (Round MFD)
I look forward to hearing from others who are willing to try this on their own oval or round MFD displays.

Note: This reset process does NOT apply to the Polaris MFI or NGI watercraft displays.
Polaris MFD Engine Hour Counter Reset (engine off)
Polaris MFD Engine Hour Reset (Tachometer active)
How to reset the Engine Hour counter on the Polaris oval MFD display
For reference, here are the original Polaris instructions for the Oval MFD display.
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This method is experimental (but seems to be working on each MFD display I have tried it with, so far). There are several unanswered questions regarding what exactly the various reset sequences (also known as CALibrate) actually do.
It has been documented for some time now how to 'reset' the MFD display to 'correct' an inaccurate voltage reading (LoPWR) on the MFD display. In my case I often ended up with a working but UNcalibrated voltage reading. For me, the result was typically that the MFD reads 1 to 2 volts HIGHER than the actual battery voltage. Until recently I had not done extensive experiments to determine why this was, or how to get a more accurate voltage reading on the display.
In the attached videos, the actual battery supply voltage was about 0.75 volts lower than the 13.9 that is displayed. Actual was just under 13.2 volts, measured with a Fluke 23 III.
Update: See this post. The MFD volt reading will only be accurate if the actual battery voltage is exactly 14.00 volts during the calibration.
If the battery voltage during calibration is less than 14.00 volts, the display will read high by the difference. In the example above, the actual voltage was 13.2 volts so the display read high by; 14.0 - 13.2=0.8 volts.
If the battery voltage is above 14.00 volts during calibration (such as when the engine is running) then the resulting voltage display will read LOW by the difference. If the charging system was providing 14.5 volts during calibration, the MFD will afterwards read 14.0 - 14.5 = - 0.5 volts (so the readings on the MFD would show 0.5 volts LESS THAN the actual voltage).
Note: This was initially tested on the oval MFD that I had on hand, from a 1997 Polaris Hurricane watercraft (model 3280224).
I have since successfully reset the Engine Hour counter and calibrated the voltage display on the following MFD part numbers;
3280252
3280202
3280147 (Round MFD)
I look forward to hearing from others who are willing to try this on their own oval or round MFD displays.
Note: This reset process does NOT apply to the Polaris MFI or NGI watercraft displays.
Polaris MFD Engine Hour Counter Reset (engine off)
Polaris MFD Engine Hour Reset (Tachometer active)
How to reset the Engine Hour counter on the Polaris oval MFD display
If display is sleeping (more than five minutes of no activity, engine not running) press the Mode button to wake it up.
Change display to show Engine Hours (use the Mode button)
With the HOUR counter visible, press and hold both SET and MODE buttons for several seconds
Display will show CAL 0000 ==> Promptly Release both buttons
followed by CAL 0828
Now press and hold SET button only
Display shows CAL 0828, then 0832, then 0828
Note: If tachometer is active (engine is running) then display shows CAL 0864, 0868
Continue holding Set button until clock reappears or MFD shuts down or reboots itself (about ten seconds)
Press Mode to wake up display
Wait until speedometer reading settles to zero
Press Mode several times until Engine Hour mode is displayed.
Should now show zero hours.
Tip: Press Mode to display battery voltage.
Use an accurate Multi-meter to measure the actual battery voltage at the battery posts and compare to the displayed reading.
Even better, touch the multi-meter probes directly to the Red/Purple and Black wires that feed the MFD display. These connections are inside the electrical box.
MFD Red/Purple wire is connected to one end of the 1/4 Amp glass fuse, all by itself.
Change display to show Engine Hours (use the Mode button)
With the HOUR counter visible, press and hold both SET and MODE buttons for several seconds
Display will show CAL 0000 ==> Promptly Release both buttons
followed by CAL 0828
Now press and hold SET button only
Display shows CAL 0828, then 0832, then 0828
Note: If tachometer is active (engine is running) then display shows CAL 0864, 0868
Continue holding Set button until clock reappears or MFD shuts down or reboots itself (about ten seconds)
Press Mode to wake up display
Wait until speedometer reading settles to zero
Press Mode several times until Engine Hour mode is displayed.
Should now show zero hours.
Tip: Press Mode to display battery voltage.
Use an accurate Multi-meter to measure the actual battery voltage at the battery posts and compare to the displayed reading.
Even better, touch the multi-meter probes directly to the Red/Purple and Black wires that feed the MFD display. These connections are inside the electrical box.
MFD Red/Purple wire is connected to one end of the 1/4 Amp glass fuse, all by itself.
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