i would suggest you connect a amp meter in series with the lead to its power source and see what its drawing...it should be milliamps....if its more then the radio has a big problem..

you can work it out like this...

if your battery has a amphour rating of say 50 amps and the draw you measure is say 1 amp (if it is its sersiously wrong!)

battery amp hours / drain = length of time from fully charged batter yto flat battery so...

50/1 = 50 hours from charged to flat...

but that wire should draw maybe 1/10 of an amp ish (not checked but thats about what i would expect!) s ofrom a 50 amp hour batter you would be talking 10 days or so...