ive removed my audio 20 radio with cassette from my 2003 w211 and fitted a blaupunkt dab unit . i bought special leads because there were no iso connections .i connected the aerial cable via an extension lead (in rear screen) but it does not amplify the signal i assume the amp must get its power from the audio gateway but i cant see how.ive checked the fuses for both aerial and gateway in boot but cant find anything wrong. any help please