No power to rear radio unit located in trunk( Becker split system
 

I have traced the reason for the radio's failure to function to no voltage present at the power connecter to the trunk unit. I've checked the only fuse I can located which iw #22 in the main fuse panel on the driver's near the braker system resevoir.
Questions:
1. Are there any other fuses in the power circuit ?
2. Any other trouble shooting suggestions ?

Many Thanks
Harry Hughes (registered user) need all the help I can get