Hi Till.

My antenna has been replaced with one that combines cell phone and radio antenna (this was before I got the Empeg).

This kind of antenna almost always needs some sort of antenna amplifier. That is usually built in, but still needs power to work. Find out how to feed the antenna control line of the tuner module (or any other switched 12V source that is appropriate) to the +12V input of the antenna's amp.

cu,
sven

PS: In your case as well as in mine (with radio/GSM/GPS combo), I would suggest to use the ignition-switched 12V line.

proud MkII owner (12GB blue/green/smoked, was #080000113 is #090001010)