as swingline said it sounds undoubtedly to be an alternator problem. most auto parts stores offer free alternator checks heres a very short list of those that do (Advance auto parts, Checker) told ya it was short. anyways if youve got a diode problem and your alternator is pumping out AC current that can damage quite a few vital components. as i work at valvoline, We offer free systems checks with our Interstate ED-18 its basically an electrical diagnostics tester it tests cranking output, alternator output, and entire charging system problems. i would personally recommend that if you are to replace your alternator you get an autolite with their lifetime warranty ive used my warranty twice, once was my fault
