wiring second radio and noise

Hello all,

Our aircraft (Ms 893E) is wired with one VHF comm (old Narco 11A - but
functionning with noise mind you). We decided to install a new comm
(found an Icom A200). The present setup is wired to a hard wired (no
jacks just wires) Telex intercom TC 200. We have two problems.
The first is the noise from the beacon-strobe in the audio system. I
will be working on solutions found on this group namelly ensuring that
the existing jacks connectors (both pilot and copilor are properly
grounded to intercom ground, not the aircraft frame. Further ensuring
that insulating washers are fitted to the jacks.

The second problem is that we do not have an audio selector panel
installation. Not being an avionic technician, I wish to know how to
connect the new radio parralel to the old. One would suppose that a
sort of "selector" switch for the microphone would be appropriate in
order to select on or the other tranceiver in order to transmit. The
"receiving" can be done simultanuously using volume control to
"prioritise".

Any comment or help woud be welcome

Marc Arsenault