Battery draining....Fuse 21 culprit (E30)

[///M3Mike]

I'm stumped.  Alternator rebuilt last week....new battery last week, as well.  Battery started dying overnight and at work.  Through test light and pulling fuses, I have narrowed it down to fuse #21, which according to my Electrical Troubleshooting Manual powers:
- Auto-charging flashlight
- Ignition key warning/seatbelt warning
- Interior lights
- Radio/antenna
- Trunk light
- Multifunction clock
- Service interval indicator

Individually, I disconnected the interior lights (glove box and courtesy lights), radio, trunk light, OBC, and the entire cluster......test light stayed on. :mad: FYI I don't have the flashlight (always had a piece of foam covering the contacts), my antenna has power disconnected, and I didn't know a way of disconnecting the ignition key or seat belt warnings.

Keep in mind, for the longest time now I have had the alternator light stay on immediately after starting, but it goes away after revving to 1500-2k.  The belt is tensioned as much as it can go and has only a cm or two deflection...it is an OEM belt, not a parts store brand.  Oh, and about 6 months ago I cleaned the chassis grounds at the alternator, engine block, and trunk-mounted battery.

Also, I have nothing exception electrical-wise: Airbag system is completely removed, I put in a full 13-button OBC, and also added premium sound from a 325is.

Is there something else drawing power off of fuse 21?  Or is this indicative of some other massive electrical problem.  Help!!!

[DesktopDave]

I'd suspect that trunk harness for a supply wire short near the hinge.  Check the door switches carefully too.  Water in the pillars can corrode their contacts.  They're easy to get out.

If I've read your post correctly, your tests have eliminated the each component, but  it won't determine the problem if you have a chafed or pinched positive  supply wire.

Pull each component and do a ohm or continuity test on their positive wires to a good ground until you locate the bad circuit.  That way you're testing the good circuits one by one until you find the short.

[///M3Mike]

Looks like I have a fun filled weekend

It's probably just a confusion of terms, but what do you mean by trunk harness?:confused:

Forgot to mention, I have been experiencing glitches with my tach and MPG-meter where they don't always work right away until I give the dash a good smack sometimes.  Moreso the consumption gauge than the tach.

Thanks for the reply!

[DesktopDave]

The wires that power the license plate lights and trunk interior light.  They run up the driver's side trunk hinge.  More of an e36 problem, but you never know.

The tach & instant MPG might be a loose grounding nut on the back of the cluster.  I think every e30 has cluster problems...I have issues with my speedo when it gets cold; it makes the instant MPG slowly sweep back & forth from 40+ to 0 and back again.

Mine is likely the plug I swapped on the diff, been too lazy to patch it up.  I don't watch the speedo anyway...

[///M3Mike]

Ahhh.....I'll be sure to check those.  

Funny you mention the grounding nut, because I JUST tightened those last weekend to see if that would solve my periodic tach troubles.  Haha.

Thanks for the responses, Dave!!

[kenika65]

front left head light area my harness rubbed to ground

[monty23psk]

I had the issue, it was the SI board. If the batteries go bad, they will drain the battery trying to re-charge them. Do you ahve the SI lights on when the car is off?

[///M3Mike]

I had the issue, it was the SI board. If the batteries go bad, they will drain the battery trying to re-charge them. Do you ahve the SI lights on when the car is off?

SI lights are not on when the car is off.  I probed the batteries when I had the cluster out last weekend and they showed a little over 3 volts each.  Not sure if that was both combined since they were still soldered to the board and I wasn't an EE major.  Haha

[///M3Mike]

Well, didn't get a chance to do much garage time this weekend, but I DID notice that the driver's side fog light comes on with the parking lights, fog light switch off.  If I turn the switch on, the passenger side comes on and the dash light lights as normal.

Weirdness continues. :confused:

[DesktopDave]

SI batteries sound OK.  That foglight is an odd one...and there isn't any really advanced CAN bus stuff going on in an e30...you have some spaghetti in there to dig out...

Keep in mind that mostly any other body e30 harness will fit that car...the engine harness is the only fairly unique part.  It's not as much work as you'd think to get that harness out, I could do it in a weekend with no trouble.  Is it better then tracking wiring faults all over the car?  Might be...

[///M3Mike]

Solved the mystery of the draining battery.  I got rear-ended a few months back and it tweaked my rear panel, bumper, and trunk.  Looks like my trunk light was staying on.  Weird that it wasn't a problem until recently, but now I can happily say that with fuse 21 in, ignition off, etc. I'm showing somewhere around .01A current draw.  We'll see what an overnight park does.

Now on to the crazy ass foglight.  I noticed my city light isn't lighting up (Euro smilies) on the drivers side even though the bulb is good.  Looks like it'll be an easy find once I pull the headlight out.

[DesktopDave]

Glad to see you found the trouble.  Good of you to post it...IMHO all problems are little after they're solved.

That trunk switch is a really bad design.  Mine won't be killing my battery...it won't turn on unless I nudge the switch.  I'm figuring that's a good place for an LED, I'll fix that all up when I get to it.

[///M3Mike]

Thanks for all the tips and thank GOD I didn't have to redo the harness.

I managed to figure out the city light/fog light issue tonight.  I won't say what the problem was, though, so as not to incriminate myself.

BTW, anyone ever notice that the connectors for fog lights and city lights are EXACTLY the same?