electrical weirdness

[funinthesun]

I have a 2003 Rinker 312. All of a sudden, my VHF radio stops working. I checked the breaker, it's fine. I pulled the radio out, and use a voltmeter across the red/black - I get 12.76 VDC. When I switch the leads, it's -12.76VDC. So that looks good. I replaced the radio. Same issue. Take the original radio, connect it to the cigarette lighter outlet at the helm - works fine - old or new radio. These leads also measure same voltage. So.....if I'm getting the proper voltage, why wouldn't it work the radio?

thanks,
Ed