The problem you are describing has nothing to do with the master/slave power settings and the yellow wire.

How are the displays connected to each other?

To share charts the units must be networked together through the Ethernet ports. Charts will not share thru a N2K network. If the two displays are connected with Ethernet and still not working, master reset both(backup everything) reinstall newest software and see if that fixes it. If not, ensure your ethernet cables are good, otherwise, get Navico involved, possible hardware problem.

They are connected via N2K and ethernet. Both displays are getting radar data just fine. I had an authorized installer put in the helm display, I later added the display at the nav station myself. I was wondering if I missed something during the installation. 

Jim, I have two very similar Simrad NSS evo2 MFDs sharing all sorts of charts both ways, and they've continued to do so through many software updates. So I think that William may be right that there is a deeper hardware problem. But before calling, I suggest you check that both of your MFDs are loaded with same and latest software, and you might also look into the Setup/Advanced pages on each. I don't think there are chart sharing controls there, but there are many on/off switches for various functions so worth a look just in case.

It is not mentioned if by any chance one of the MFD's Ethernet is cabled through a Wifi1 GoFree device.  Some installers do this as it looks like it is designed to do so - the GoFree has two network ports on it.  However, it is lousy switch.  GoFrees should only be connected as a single line to a plotter or a NEP.  If you have a GoFree in your network and it is being used as a switch (ie., both of it's ports are occupied) then try recabling the layout.  You might find that this will clear up the issue.   Also make certain that both MFD's are running identical software versions.

What issues have you seen with the WiFi-1 used as a switch?  It's sitting between my Zeus2 9" and 4G radar and appears to work fine.  That is, after Navico replaced a bad out-of-the-box ethernet cable (1 wire open).

Doug - main issue has been general instability.  As a rule we don't run other network items through a WiFi1.  In  most situations if we are onboard a vessel that is having erratic network behavior (radar dropping out... ie "No Radar" messages, or radar trigger issues), or really any Ethernet issues, and the vessel has been wired with the WiFi1 as a switch, the very first thing I do is rewire to bypass it.  Of course if you cannot complete your network without adding an NEP this can be a problem.  Your Z2-9 has only 1 Network port on it, so if your setup is radar and a WiFi1 then you have no choice.  If it is working OK then let it lie.  If the radar ever gets wonky on you the first step should be to bypass the WiFi1 and wire the radar directly to the Z2 and see if the issue goes away.

I have seen this issue where an installer ( Hans' US agent ) connected 2 displays to a WiFi-1.  It worked as long as the owner started the devices separately with the radar off.  I suspected bandwith and added a NEP-2.  No more problems.

The other possibility is that the WiFi-1 is really REALLY slow to power on.  It MIGHT be that this configuration will work IF its yellow switch wire is not connected to the display power up bus, but is wired to live and the displays are not enabled till it is powered up.  I don't like this solution as there is always the worry of having to do things fast and not having the maps you need in an emergency.

The WiFi-1 does have an option to allow it to act as a switch for it's two Ethernet ports.. It was really designed to connect to a WAN network. However....  it is not a very fast device and if there is already lots of traffic ( as in start up ) it does NACK a few packets.  I don't think the map sharing is as resilient as it could be and the NACKed packets seems to kill it.

Remember the WiFi1 was designed to cope with usable WiFi bandwidth in the order of 5Mb/s where as the Ethernet on these devices is 100Mb/s.

The other thing I have seen people do is use the second Ethenet port on a Zeus 12 as a Ethernet hub.  It suffers from similar bandwidth problems.

As others have said a NEP or even a Sonuhub  will likely solve the problem as that has an Ethernet switch.

I just wish there was a larger and faster NEP device!

Mub

Well, there kinda is a larger and faster NEP device.  The NEP is nothing more than a marinized Ethernet switch.  And it's got a bit of a tubbish chassis.  We've done numerous installs with Netgear 12v switches in lieu of NEP's and they work just peachy.  They typically have 6 or 8 ports.  You can either cut the Navico network cable and install an RJ45, or if you want to be all belt-and-suspenders about it you can use the Navico Ethernet to RJ45 adapter cables.  Either way works fine.  

I've had some bad experiences with the NEP and connecting it to upstream switches. In at least 5 cases, I have removed the larger NEP-5 and added a Netgear or other switch to alleviate weird network and performance issues.