Ok here's a strange one. I have a Grand Rapids EIS-3 on my 582 powered IV. The other day the EIS would not come on when the Master inst. switch was thrown. After checking all the connections, grounds, ect and finding nothing I happened to push the PTT switch on the stick. Well what do you know the EIS comes on when the PTT is held. I'm really scratching my head on this one ? I know the EIS is hooked to the intercom system so that an audible warning will go off in your headset should you exceed the preset limits of various readings. What I can't figure out is exactly how and why pushing the PTT enables the EIS to power up ? Anyone ever had something like this happen with their EIS ?