Cannot say right not, have not done enough research. The J1939 uses a protocol which NEMA, 11783 and NEMA 2000 also can use. One is 8 bit and the other is 16 bit, but from initial thoughts is may work. The issue (IMO) you run into is that the MEFI 3 ECM does not talk to buss, so the interface of who is getting the correct readings may be an issue.

Exp: If the J1939/NEMA reads that the motor is overheating, does an alarm sound for the ECM (which protects the motor) or the NEMA display. Far out example, but hope the drift is caught

For Mercruiser -- ECM 555 and PCM 555 and PCM 09 and on yes , MEFI 1 and 2 and 3 nope.

Looks like you need a converter/gateway for older motors. I have MEFI3 motors myself and would love to do an in-dash plotter with engine monitoring.

Looks like this is the ticket.
http://fox-marine.com/index.php?rout...&product_id=55

Instructions from Raymarine on how to use it.
http://forum.raymarine.com/showthread.php?tid=552

Have never seen that before thanks for posting. I still would think if one would call Merc their answer might no as well for MEFI 1 -3. So that post above is good to know

Also found these that are more of a true "analog to digital" converter. Basically wire right to analog gauge senders and you can program the unit for each particular channel.
https://www.navstore.com/engine-syst...ing-interface/

Thanks for all that info. I have something to go on and reading about these components I have a good idea where I need to go with my idea.
It looks like the converters are the real time data stream and the best for me. The updating type means processing and I don't want that in the way. Converting right off the sender to NMEA 2000 looks like the way I would go since it is more like live analog.
I still want to talk to Merc to understand more about their communication protocol. Finding that out could also help me to customize the conversions.
You guys have been an immense help. Thank you all big time !!!!

I have 05 500efi engines and I am in the same situation. I called Merc with the engine serial numbers and was told no smartcraft capability. I was looking into the Noland units as I am planning on keeping most gauges and running a Simrad Go7. I will watch to see what you decide on.

I like the look of traditional gauges but the graphics of some of the display units have a very real look just like the real thing. Once I talk with Merc I will know the comm protocol and know how to move the data for gauges. Another benefit of going network is getting a lot more data than just simple instrumentation. That is very practical to me and makes me lean in the direction of dual displays for everything.

Can anyone verify what protocol the Mercury (Motorola) ECM555 communicates via. Is it the J1939?

Pretty sure that would be the CAN protocol. The Merc gateway mentioned earlier converts CAN to NMEA 2000.