Roy Page wrote:

Maybe the old owner was correct ?

If he is, then something isn't wired properly. The first thing I would do is get
a schematic for the intercom wiring harness and check the power line for power
with the avionics master off.

George Patterson
Drink is the curse of the land. It makes you quarrel with your neighbor.
It makes you shoot at your landlord. And it makes you miss him.