[Jade]

Where I get confused is trying to add a DSC VHF. having it listen to the GPS for position seems straightforward enough, but how do I make it talk to the GPS when it gets an emergency call?

You're right; it is definitely confusing!

I skimmed through the on-line manuals for your GPS and DSC VHF and found the following:

Your DSC VHF sends out two NEMA messages when a distress call is received ($CDDSC and $CDDSE) using NEMA version 3.01. These are sent on the NEMA + (Green) and NEMA - (Orange) wires on the GPS/Alarm cable bundle.

Your GPS can receive DSC emergency info using NEMA version 2.3. This may be problematic so some testing on your part is required. (The Garmin manual does not mention which DSC messages types that it recognizes.) You may connect the DSC VHF directly to the GPS input 1 NEMA + (#4 brown) or input 2 NEMA + (#5 white) and NEMA - (#2 black).

If you choose to route through the ShipModul 41BT then you might consider the following:
- Wire the DSC VHF Green and Orange to an unused NEMA IN port on the multiplexer. (This will allow the VHF to broadcast its DSC messages to all devices connected to the ShipModul.)
- Wire the GPS (#4 brown and #2 black) to the NEMA OUT on the multiplexer. (Up to four devices can be tied together on each NEMA OUT port on the multiplexer.)

I have not tested this setup so I strongly recommend that you check your manuals to verify the wiring and test it well yourself.

LOL