Battery drain from Fuse 21... WTF?

[CorvallisBMW]

I finally traced my battery drain to something attached to fuse 21. Unfortunately, according to the Bentley, Fuse 21 powers THE ENTIRE FUCKING CAR. Seriously, here's the list of everything that supposedly runs off of a 7.5A fuse:

Glove box light
Glove box flashlight
Ignition key/seatbelt chime
Interior lighting
Radio memory
Trunk light
Check panel
SI lights
OBC
Fuel Delivery (fuel pump?)
Tach/MPG gauges

How the fuck can all of this stuff run off a 7.5A fuse? That's impossible.

1) What is actually run off this fuse?
2) How do I track it down?

[Das Delfin]

That's all low current stuff so 7.5a should be plenty for all of it. I'd def start with your radio if it's aftermarket. The glove box lights/trunk light shouldn't be too hard to check either. Try changing or removing the bulbs

This guy is pretty helpful

https://www.youtube.com/watch?v=KF1gijj03_0

On our cars some circuits are run through multiple fuses so if a system controlled by fuse 21 also runs through another fuse but doesn't cause a current drop when you pull its other fuse, you can eliminate that system from your fuse 21 list

[CorvallisBMW]

Good point about the multiple fuses, i didn't think of that. I had seen that video before and actually used it as instructions for the draw test. Right, off to check more stuff...

[sheldpaugh]

Ever figure this out?

[CorvallisBMW]

No, in fact it's left me stranded once or twice. I need to tear in to it this weekend ASAP

[george graves]

The hard thing to see are things that don't make light.

So, forget the interior lights, but that monster stock relay can. They get warm when they fail. And warm means a draw.

Anything drawing current will get warm - if it's popping a 7 amp fuse, then it's using almost 80-90 watts. Watts= Volts * amps - and as you know, that means heat.

I had a bad trunk light switch once. Easy test, put your phone on video record, and close the trunk. Some times the switch will turn off when pushed, but not when closed.

[CorvallisBMW]

hmmm good idea. I'll try that. I also wonder if the glove box light or flashlight socket could have something to do with it. I've been rooting around in the glove box doing so much wiring lately that I may have inadvertently crossed a wire.

[Cephas]

SI lights seem to be the most likely culprit here. Check everything else, sure, but when is the last time that you took the SI board out and inspected the batteries?

[2002jm]

pm sent

check back up lights:)
jm

[CorvallisBMW]

SI lights seem to be the most likely culprit here. Check everything else, sure, but when is the last time that you took the SI board out and inspected the batteries?

I've never checked them, but they seem to work OK

check back up lights:)
jm

Got your email... they don't come on unless I actually have it in reverse, but I will check the wiring.

[CorvallisBMW]

Battery drain from Fuse 21... WTF?

SI board batteries seem to be in good shape, but I am getting a ~150mA draw from the blue connector on my cluster. There is another ~100mA draw coming from fuse 21 in addition to the IC draw, but I cannot locate it. I disconnected everything that is related to it (trunk lights, glove box light, interior light, radio fuse, trunk light, check panel, OBC) and none of them changed the draw. I disconnected the reverse light wiring as well and still no change.



So the IC is responsible for at least part of the draw, but it's not the only culprit....

The batteries themselves are showing 3.1V each, and I'd like to take them out and check amperage but they appear to be spot welded in place on the connectors... each + and - tab on either end has 2 small dots that look like spot welds almost? I don't want to break anything by prying on them.

[CorvallisBMW]

Anybody? This is driving me insane. I've also checked all the aftermarket stuff (alarm, headunit, amps, etc) and still nothing. by cluster draws 150mA and something else on fuse 21 draws another 100mA, but I've checked everything listed in the Bentley as being on fuse 21 and none of them are drawing power.

[AndrewBird]

Those are in fact spot welds. The batteries come with the tabs welded on because you can't solder to lithium cells, they explode. ave to desolder the tabs from the board to remove them.

If you buy new batteries, I can swap them out for you if you can't solder.

[CorvallisBMW]

I'm still not convinced that the batteries are actually bad; they show zero signs of being dead. 48 hours after pulling the SI board out they still show a solid 3.1V each, so they're not draining. So if they were bad enough to be drawing 150mA of current, they'd be totally dead after 48 hours, which isn't the case. But what else in the cluster could cause a draw that big??

[CorvallisBMW]

SI batteries are still at 3.1V, so I'm not suspect of them.

Checked the hazard switch, negative
Checked all the trunk lid wiring (brake light, luggage lights), negative
Checked the small alternator wire, negative
Checked the door wiring, negative
Checked the door triggers, negative
Checked the alarm/keyless, negative
Checked the amps, negative
Checked the deck, negative
Checked the OBC, negative
Checked the check control panel, negative

Totally out of fucking ideas... :(