Audio and Sat Nav power question

[scottb721]

I've run the YR wire (12vACC) going to the McIntosh HU through a relay that is operated by my mobile phone's car kit mute.
Make or receive a call and the Mc turns off. Works fine accept one thing - it also powers down the Sat Nav screen.

The screen ACC isn't spliced into the YR wire so I've ruled that out.

Any ideas why this might be happening ?

Leaving the Mc's Nav plug disconnected prevents the screen turning off. I don't use voice guidance so may try this method although I'm not sure what else the nav plug does.
Thanks