Marine Electronics Forum - Adding an external GPS antenna to a Garmin

I just bought a Garmin 172c with internal antenna to replace an old 162 mounted in an electronics box under a hard top. I thought the 172 came with the BNC port to connect with an external antenna but I was wrong.
I'm thinking of putting a female BNC connecter on the GPS (there's a place for it on the back, just not cut out) and moving the wires inside the unit from the internal antenna to the connecter.
Any thoughts on why this wouldn't work?

Two things:

1) Are you sure the 172c won't work under the hardtop? It's true the older units don't work as well through/around obstructions as the newer ones, but still, try it if you haven't.

2) If you decide you need to go ahead with your project, it should work IF the existing internal is electrically compatible (actually, identical) to whatever external you plan to hook up. I have never seen the internal antennas, and don't know if they are just a sub-unit with coax connection to the rest of the unit (in which case, it should work) or something else. Let us know.

(I did disassemble just for drill the only Garmin GPS I have ever discarded, but it was an external antenna unit.)

On many early Garmin plotters the "internal antenna" was under a back cover, and used a standard BNC connection. To flush mount the unit, you removed the back cover (it isn't sealed) and plugged in the GA29 antenna. So look; if there are a couple screws holding the back cover on, and it isn't sealed with a gasket, try it.