1991 honda crx dx models showing trouble code 20, alt. output is14.18 and a brand new batt. Which shows 12.93 volts but if I turn on the headlights the tach. Drops to 0 and the temp. gauge goes all the way to hot but the alt still puts out14.08 volts. Another thing is if the lights are off and you turn on the blinkers the temp and tech. bounce with the flash of the blinker . I know the book tells to take it to the dealer but you guys seem like you know a lot so I figured I'd give it a shot by the way this is abone stock car not all cut on or rigged up original millage on the car is 60012 and have owned it since 93 it has been used very little in last 15 years

The solution will likely involve either replacing the Electrical Load Detector (ELD) in the under-hood fuse/relay box or the ECM.