Hi Pat, et all;
Looked up my NEMA wiring hookup_
a. ICOM502A.............NEMA IN = red
................................[RMC, GGA, GLL - supplied from 2006c]
b. ICOM502A.............NEMA OUT = white
................................[DSC, DSE - supplied to 2006c & C80]
c. GARMIN 2006C........NEMA IN = violet
..................................[DSC, DSE from 502A]
d. GARMIN 2006C........NEMA OUT = grey [channel 2] [RMC]
..................................[ RMC, GGA, GLL to 502A; RMC to 3100]
e. RAYMARINE C80.......NEMA IN = white
...................................[DSC, DSE supplied from 502A]
f. NAVMAN 3100...........NEMA IN = yellow
..................................[RMC supplied from 2006c]
g. NAVMAN 3100..........NEMA OUT = white
..................................[not used]
The new(2004) 'Installation Manual" for the 3100 does reflect the above wiring hookup on page 17 & page 19, Appendix A.
Common signal NEMA ground for all units is their 'black' lead.
Both the C80 and 2006C has a GPS receiver.
The drawback from this setup is that I can not directly transfer waypoints from the GARMIN to the C80; which would be very convient. I suppose I could create an 'A:B' switch for data transfer in place of the 502A, to the C80, from the 2006c.
The advantage of data from the 502A is that any Distress Call that is received on the 502A will be seen on the 2006c, and on the C80.
The C80 also has SeaTalk hookup for the ST6001 S1G Autopilot.. If I had a means to connect into the SeaTalk module, I think I could transfer the GARMIN waypoints at will; but, I am not sure enough to take on the cost for the added interface.
Does anyone have a similar setup? Has anyone attempted this?
Hope this is clearer enough to help.
I did get

shocked when I lost my 'range' function on the 3100 last weekend. The 2006c channel2 NEMA port was disabled. I must have been playing and not paying, 'attention'. One of those suttle little thingys that will get you every time.
Happy, healthy and prosperous New Year.
sea Angel