I have a battery drain that empties the charge every 5 days or so. The guys at Autozone said I have a .5 volt loss when the car is off. I know the ECM and radio use a little but not enough to drain a battery. Is there any way to trace this drain and if so could you give me a detailed description of how. I am decent with wrenches but :confused: with electical stuff.
:crazy: :rolleyes:

85 Aquamarine

 

You could hook the test light up to between either posts and pull the fuses one at a time until the light goes out. Leave the last fuse that turned off the light out and start putting the fuses back in one at a time until the light comes back on. This will tell you what circuits are drawing power. The only way to tell how much would be to put a meter in the circuit after they are identified.
Hope this helps.

 

Actually they were close, battery drain is in Amps, the unit of current flow. But in any case it's not difficult, just unfamiliar territory.

Go to Radio Shack and get a decent Digital Multi Meter (DMM); read the manual and get familiar with the tool. Trouble shooting principles are the same, isolate and identify!

If your battery has a rating of say 60 Amp-Hrs and it goes dead in 5 days (120hrs) it means the current drain is 0.5 Amps or less (likely less since the battery has some charge, i.e. residual voltage reading under load). The ECM, radio, alarm, etc likely draw less than 1/10 that much current when idle.

Make sure the ignition switch is Off.
Disconnect the + battery cable, set the DMM to the highest Amps scale, connect black lead to battery cable and the red lead to the battery + terminal.
Adjust the Amps scale if necessary and record the current drain.
Then one by one, pull each fuse, noting the resultant current reading on the DMM (start with the ECM, alarm, radio fuses).
When you remove the fuse to the trouble circuit, the drain current reading should drop substantially.
Then disconnect the DMM from the battery, leaving the battery disconnected.

Once you isolate the problem circuit, you use the resistance (Ohms) scale on the DMM to check for leakage paths to ground.

Caution, do not measure resistances through the ECM or the digi dash.

Of course you could just pull each fuse in turn, waiting 5-6 days to see if the battery survived till you find the trouble circuit and then look for a shourted wire. But I don't have the patience for that either.

 

Thanks guys, this will get me started and you simplified it tremendously. :cheers:

85 Aquamarine

 

My 85 has a drain on the radio/amplifier/doorlock circuit. I've just got the fuse pulled out for now. I think I remember reading where the early C-4s had a problem with relays for the Bose speaker amps over time (?).
Good luck,

Carl