The easiest way to install a Hour Meter is go to like West Marine and buy one for like $10.00. Be sure it is for marine use. Then either in the engine compartment or under the dash area near the meter installed location, find a "Purple" wire and connect the Positive+ end to that wire, and a suitable Ground-. The purple wire is only energized when the DESS is connected which is accurate for engine run time. If you want it accurate, and you can get the use hours off your engine from a seadoo dealer, just bench run your hour meter( attach it to a 12 volt battery on a bench) to the correct engine hours then install it.
Karl