Battery Drain - Long troubleshoot, looking for advice

[Rtheriaque]

Hi folks,

I have an '89 325i. I replaced the alternator and battery in June. The battery was 12 years old and the alternator tested as bad. After replacement everything was great.

On the 4th of July I did the v-belts. I did pull the alternator at that time just because I found it easier to slip the belt on. I had disconnected the wiring. The battery was disconnected when I did this work. The car worked fine on the 4th and for my commute on the 5th. On Saturday the 6th I left for vacation and the car sat for a week.

On return, the battery was completely dead. Even the clock wasn't running. I jumped the car, drove it around and did some errands (including shutting the car off). It started right up and everything seemed okay.

Until the next morning... Dead battery again.

I checked the voltage at the battery with the engine running at about 2500 RPM. I got 13.7V, which is good. The battery charges and holds when it's disconnected. I could have that tested separately, I suppose.

With the car off and all interior/glove box/trunk lights out, the car has a drain of .54A. Yikes. I started pulling fuses. Fuse 21 drops the voltage right down to .02A. That's a busy circuit:



So, I popped the head unit out (stock). With the red/green wire disconnected (Fuse 21 back in place), the drain drops to .14A. It looks like the head unit might be the culprit.

Questions:

What should the draw be on a good car?

What is the typical draw of a factory head unit?

Does anybody have any further ideas/advice?

[kbeefy]

Excelent trouble shooting!

I don't know about these cars as I'm new to BMW's, but in other cars .05 seems common for the ECU, clock etc.

Any drop on any of the other fuses?

[Rtheriaque]

The radio's red/green was definitely the culprit for the overnight drain, at least. Car fired right up this morning.

Oddly, the radio is fully functional. So... I have no idea what's going on.

[dogsbark26]

I don't know either but... does your power antenna work? Could it be that the radio head unit is trying to signal the antenna to retract?

[Rtheriaque]

Power antenna is fine. I disconnected it while monitoring the amperage- it's not contributing to the drain.

[Mopri]

have you seen your ground cable that´s near the alternator? is it ok or it shows some wear..?

[Rtheriaque]

Looks okay... Why would that cause the radio memory to draw so much amperage?

[Gregs///M]

red green is memory power input. A short in the radio will cause this to drain more than normally, such as a failed component. Fantastic job troubleshooting, that's how it should be done.

[Rtheriaque]

Thank you for the input. I appreciate the compliment. The "noob" tag next to my name bothers me a bit- my first E30 came at a time when a significant portion of this board was likely in diapers! It ain't my first rodeo and I take pride in my vehicles. I'm not one to come here with a clicking starter solenoid asking if my battery is dead!

I currently have six separate factory radios in my garage that I've put together to make one that was "perfect." Looks like it was in that state for about three weeks before the heat killed it. Disappointing...