Hi, I have a Furuno GPS-32 that has been successfully interfaced to a
PC for navigation for quite some time. Now I want to hook up the GPS
output to a Uniden Polaris VHF.

My puzzlement is because the Uniden shows one wire for GPS Data In and
the Furuno is expecting two wires.

Looking at the Furuno connection diagram

The Furuno has connections labelled SD and RD that go only to the PC.
It has another connection labelled TD-C/SG which the diagram says to
connect to both the PC and the "RD-C" connector of another device like
a radar (and I presume a VHF.) I'm guessing that C/SG means
common/signal ground The fourth Furuno connection is to be connected
to the "RD-H" connector of the other device. I bet that means
Receive-High.

The Uniden connection cable has one wire for "GPS Data In." It also
has a ground wire. The RD-H connector on the GPS obviously goes to the
"GPS Data in" wire on the Uniden.

How does the signal return to the Furuno? Does it go through the -12v
wiring? Or should I connect the Uniden ground wire to the TD-C/SG
connector?

Thanks for any advice