Mine has the (older) inline paddlewheel senders back near the fuel tank. (they work YAY!!) Pretty sure my motors are pre - NMEA2000 and I have heard (but cannot confirm) that the newer Yamaha has the fuel usage sender under the cowl.
The in-law's boat has that same style sender and I believe the engine is a 2003?? I believe it runs on NEMA0183, you'd be surprised at the crazy adaptors and converters available if you're willing to do a little digging. I rigged a boat not that long ago with new Furuno TZ touch screens, their top of the line, and we were able to splice, convert and integrate a 10 year old NEMA0183 Raymarine digital compass that the user insisted on having lol.
I'll have to do research too see how the newer yamis do fuel calculations, all I know is I still have a separate screen in the dash. I'm thinking of replacing all my gauges with a 7" Garmin and integrating the engine data. But I suppose I should get the boat back from the fiberglass shop and into the water to make sure it all works first!!
CDS or DDT, I can't afford either. What does Merc use now?
DDT was the grandfather of Mercs computer diagnostic tools, came out mid to late 90's. Still works great if you still have cartridge's. CDS was their first laptop compatible computer diagnostic system (get it, CDS, haha real original). CDS was introduced in the early 2000s and was supported up until 2018ish. It's no longer supported by Merc. The new system is called G3 (no idea why they call it that, Gen 3 maybe?) CDS was a program written by Bosch for Merc to communicate with PCM's that were at the time build and programmed by Motorola. G3 is supposedly written in house at Merc and was released when Merc supposedly started programming PCM's in house. G3 is Backward compatible with all but the oldest Optimax, EFI outboards, and EFI Mercruisers. That's where the DDT is starting to make a comeback.