Starter/alternator draining my battery?

[nitrous9200]

When I bought my car, the previous owner said it had a drain that would kill the battery within five hours. As soon as I got it, I found a small 90mA draw, pulled out the aftermarket bluetooth system and the draw was back to the expected 10mA. After a few weeks, the battery was holding its charge - I thought the problem was solved.

I've driven the car more in the past few days, and the draw is back. However, it's not being caused by any fuses; a few wires are connected to the positive terminal and the one causing the 2.7 amp drain seems to be connected to the starter or the alternator. If I remove this wire, I hear a click and the engine doesn't crank, but everything else works. If I leave the wire connected, start the engine and then remove it, the battery voltage drops from 14V to 12.5. At first I figured it was the starter, but the second test led me to believe it was the alternator. I'm not able to follow the wire to its source but if it is the alternator, I can't understand why the starter wouldn't work with the wire disconnected.

Are there any ways to figure out which of these components are at fault? Some googling seems to confirm that either a bad starter or alternator can cause a drain but I'm not sure, so I'm appealing to the sage minds of ATG for help.

 

[C1]

The problem description suggests a bad/leaky alternator diode. (With the engine stopped, battery current leaks into the alternator instead of being blocked by the diodes.)

Just take the car to a reputable auto repair and have the alternator tested.

I suppose another possibility is that the starter solenoid is stuck "on", but that shouldnt be able to happen with the ignition off. Further, removing the problem wire and observing battery voltage falling to 12.5 suggests simply that you have disconnected the alternator from the circuit and that the car is simply running on battery, so that supports the bad diode theory.

Disconnect the alternator from the circuit, let the car sit for a week, then reconnect the alternator and try to start the car. If it starts, then it is the alternator dragging down the electrical system.

 

[Zenmervolt]

removing the problem wire and observing battery voltage falling to 12.5 suggests simply that you have disconnected the alternator from the circuit and that the car is simply running on battery

Or it suggests that the car is then running entirely on the alternator and the battery is disconnected and sitting at its normal open circuit voltage with no load.

A large gauge wire from the positive terminal on the battery is going to be going to the starter. The alternator is only going to be sending a couple of amps to the battery when the engine is running so it won't need a huge wire. The starter, on the other hand, will draw 150 amps or more and that will have a very thick, dedicated line from the battery to the starter solenoid.

The "click" that the OP is hearing is the low-voltage portion of the solenoid closing the high-voltage side. With the wire disconnected, the high voltage side isn't getting any current so it's not starting and all you're hearing is the click.

Chances are the wire the OP is talking about is shorting against something else somewhere along its route.

ZV