You may have a dead short IN the battery --- but because it's flat there's just some voltage without any amperage. I would disconnect the battery and take it and run a load test etc on it. Sometimes a battery can sulfate and the sulfate builds up in the bottom of the battery until it shorts out the plates.
Didn't matter if the key was in or out. I believe it may be the blower relay gone bad. I pulled the plug out to stop the buzzing and my fan still works with a switch that was wired in years ago.
It no longer kills the battery and everything works...
Finally got to take the Monte out with the 6 speed. Great easy clutch pedal and the pro 5.0 shifter is sweet. No more burning up the old TH350.
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
Hybrid Mode
