My Digital Radio power supply is marked 1.2Amps.
Recently I was shocked to see the fuse for the radio circuit in my car rated at 25Amps - I guess the manufacturer doesn't know what type of equipment that owners will install - particularly high wattage speakers.
Most of the power for your radio will be for the CD motor and the speaker(s) - The tuner piece will need very little.
You could do with one of those old fashioned motor car Plus and Minus ammeters to see what's happening...several here...
http://www.twenga.co.uk/dir-Garden-DIY,Measuring-equipment,Ammeter
Good luck...
Peccavi, March 2009
