You need to be using a seperate mic to be heard when using the bike cradle. The car cradle has a speaker and mic built in. It can be interfaced with the intercom and stereo on the 1800. But you will need to use the items I listed in a earlier post.
I have tried this on a GL1800and it works just fine.
95300 cell phone harness $25.00
Cellset model MC/BT2 $99.00
9528 intercom harness $35.00
Plug the Stereo output of the Zumo directly to the the aux input under left pocket.
Install the Kennedy harness. Plug the 2.5 mm stereo plug into the speaker input in the Zumo cradle ( it is a a mono input but it works fine.
Ride Safe & God Bless