Expert: Brad Sears - 11/19/2007

Question
1980 stock corvette. I have a draw on the battery, battery dies in 2 days. I removed the Negative wire from the battery. I then place a test light from the Negative battery terminal to the negative wire & get a lighted test light, assuming this means i have a draw. I then pulled every fuse one by one from fuse box. then any wire plugged into fuse box. Test light still on. I removed every fuse, Wires on fuse box & plug on alternator. Still a Lighted test light. WHAT GIVES???? Did not think this was possible.
What am i possibly overlooking?

Answer
Robert, all cars built in the electronic age have what we call parasitic draw. The electronic age started with the introduction of the diode equipped alternator in the 1960's. Usually the draw is less that one amp and most auto makers today say that the battery will discharge in extreme cases in as low as 21 days. That is provided that the battery has not any sulfation and will pass a load test based on it's amp hour or CCC capacity. So with that now said I would suggest a load test on the battery. If the battery passes the load test the next step in you diagnoses would be to disconnect the alternator. Diodes can leak and draw a small amount of current as well as the built in voltage regulator stays powered up in a lot of vehicles. If the draw is still there then it is time to get an ammeter into the circuit in place of the test light. Most digital volt ohm meters have provisions to run a 10 amp maximum amp test. On your Vette you would probably not want to see a parasitic load of more than a half (500ma) draw. Do you have an alarm system, a remote starter, or Lojack? They all draw current when the car is not running. But test the battery before tearing the car apart.
Brad
Brad