Thanks again Dave. At this point, I'm still deciding if I really want the autopilot, but leaning towards it. (Kind of a big expense for a want vs. a need...) I got a reply from Garmin about how the two GPSMAP's would interact via NMEA 2000, and still trying to wrap my brain around that.

I'll copy and paste their reply to my question about putting both units on the 2000 network.:
Dear Colby Smith,
Thank you for contacting Garmin International. I'll be happy to help you.
The GPSMAP 541 is NMEA 2000 compatible as well and can be added to your
existing NMEA 2000 network (drop cable and t-connector).
When connected to the NMEA 2000 network both devices would receive data
that is sent using the NMEA 2000 protocol. It's not shared over the
Garmin marine network, because the 541 is not a network device.
So both devices can be set up using the NMEA 2000 network and see the
same data (AIS and DSC) from a NMEA 2000 compatible AIS/DSC. The same
can be said of NMEA 0183 protocol. If you wire the 541 using 0183
protocol, it will also receive the AIS and DSC data that you currently
receive with the 840xs.
If I didn't answer your question up to this point, on the last question,
"How would I access the other units data thru the unit I'm currently
looking at? " what specific data are you referring to?
With Best Regards,
Nicholas
Customer Care - Marine Team
Garmin International
913-397-8200
800-800-1020
913-440-8280 (fax) 6082
www.garmin.com
Additional solutions may be found at
http://www.garmin.com/garmin/cms/site/u ... rchsupport
>> *Original Message ...*
>> From:
mcs2442@gmail.com
>> To:
product.support@garmin.com
>> Subject: Nmea 2000 Connections
>> Message:Hello. I have a GPSMAP 840xs that I am getting ready to hook
up to a RayMarine EV-100 autopilot via the NMEA2000 connection. I
currently have the 840 also hooked up to a VHF radio with DSC and AIS
via NMEA 183. I also have an older GPSMAP 541s that I use as backup. Can
I connect the 541 into the 2000 system as well? Will the 840 and 541
share data thru the 2000 connection? Data such as the AIS and DSC
information. How would I access the other units data thru the unit I'm
currently looking at? Thanks.
At this point it sounds like I will just do a second 183 hookup between my VHF and my older GPSMAP 541. (The VHF has enough wires on the 183 network to hook up both Plotters. However the second set I will use will not allow transmission of data from the 541 to the VHF. So only the GPSMAP 840xs can transmit data to the VHF.)
If I do get the autopilot, then I would hook up the GPSMAP 840xs to it via the 2000 network, and believe I would just need to add the one "drop" cable for that. If the GPSMAP 541 cannot transmit/transfer any route or waypoint data to the autopilot, then there is no need to hook it up to the network at this time. However, the other item I am looking at, if I end up with a 2000 network, is possibly hooking my Merc Smart Guage system into it. This opens up another can of worms with what do I need to do that. I know my engine, a Mercury 115 EFI 4-Stroke is capable of smart guage; I just don't know what it takes to connect it to my GSMAP's which both have pages for engine gauges. So much for my simple C-Dory.

Colby