Battery Drain

A

acat2002

Well-Known Member
Messages
326
Reaction score
0
Location
Boston, MA
I was hoping to short-cut some lengthy circuit testing by tapping the experience on this board.

The problem is this....
After re-installing the fuse in position #4 (to work the clock and interior light), the battery drains very fast (within 4-6 hours). The dome light turns off and I disconnected the clock, yet the bettery still gets sucked dry. Now I guess I know why the PO had this fuse out :cry:
I see by the wiring diagram, it appears that only a few devices run from fuse #4, such as rear luggage light, clock & interior lights. Wiring diagram also shows a lead running to the hazard switch. I haven't checked the luggage light, but if I remember there is no bulb in there, so I didn't think to look in that direction.

the basic question is...
If after eliminating the clock as a culprit, where is the first place you'd look for a current drain?

Anyone have a similar experience?

I'm trying to avoid removing the fuse panel to expose the rear. Working in that tight space with thos hardened wires is a total PIA! I do have the dash removed, so I guess now is the time to address this issue.
 
I had a similar problem with my Bavaria. It turned out to be the light switch in the trunk. I would check to see if the switch is adjusted correctly or perhaps check the light switch in the engine bay attached to the hood. The odd thing in your case is that your battery drains so quickly, this would indicate a short; but a short would cause the fuse to blow. A battery should last all night with an interior light on. Maybe you should start with the trunk and hood light.An easy way would be to simply check to see if the light itself is warm to the touch.
Good luck!
Mike
 
Along those same thoughts....
If you can put a DMM in series with the fuse (or just in place of it) and find the draw (in amps).....
That might point you in a direction.

Again - It's odd the fuse doesn't blow. Must not be quiet a short circuit but still a pretty good draw as your battery goes flat so soon....
 
LIP, I agree that it is odd that the battery drains so quickly without an actual short. Then again, the battery is old and Boston is COLD right now, so maybe there are other factors why the battery is draining.

I hadn't thought of checking the hood light switch, but I'll check both trunk and hood lights before looking elsewhere.

My next step would be to (as you said) put the multi-meter in series (in place of the fuse) and see how much is being drawn.

We'll see....
 
If as you say the battery is old, seems like you should get it tested first before spending time trouble-shooting elsewhere.
 
+1 for the trunk. Had it on my E3 as well. Mine lasted 2 days though (fresh battery and good alternator)
Easy to check though.
Get in the trunk and have it closed by a buddy from the outside.
Make sure that buddy is not having an affair with your wife though, with the vintage of our cars you shouldn´t expect to find the anti-Jimmy-Hoffa-experience-lever on the inside that modern cars sold int the US have.
 
Assuming a savvy PO could not identify the drain, it may not be just the trunk light. We could have a byzantine failure of the hazard switch. If only one of its contacts fails it could be energizing the flasher circuit through fuse 4 while the ignition is off. You can unplug the wire that goes between fuse 4 and the hazard switch (on the back of the hazard switch) and see if that helps. (If you remove the switch altogether you'll lose your side marker function).
 
Arde, I just replaced the hazard switch (recently) but that doesn't mean that the hazard switch is not the culprit. I will check that after the trunk light.

Why does this circuit supply power to the hazard circuit? I thought the hazard switch got power from the light circuit?
 
Don't forget about the glove box light. Here is a simple trick I'd picked up on to check whether the glove box light staying lit. Put a digital camera with a motion picture feature in a close glove box, turn on mode and let it run for a brief period. Play it back, if the light was still on then the camera would've captured it. You can also employ this technique in checking the trunk light.

Also, check for a defective light/headlight switch as its power wire is connected to fuse 4.
 
Cool trick Bert!

As I mentioned the entire dash board (and glove box) is removed. Glove box light is disconected. Also...and I could be wrong...but the glove box light is on a different circuit -fuse 8- off of the power supplied to the rear defrost.

I'll post again when I've had a chance to eliminate the most likely culprit (trunk light).
 
acat2002 said:
Arde, I just replaced the hazard switch (recently) but that doesn't mean that the hazard switch is not the culprit. I will check that after the trunk light.

Why does this circuit supply power to the hazard circuit? I thought the hazard switch got power from the light circuit?
Click to expand...

The flasher needs 12V for the blinkers and for the hazard switch, but the blinkers only work with ignition ON, while the hazard works in any case. The kludgy solution they used is to route 12V through the ignition switch when the hazard switch is OFF, and route 12V from fuse 4 when the hazard switch is ON. If you replace the hazard switch then the failure is a long shot, unless they started to outsource these switches to China or something.
 
I went fairly nuts on a similar deal. On my car(D-jet) it turned out to be the fuel pump relay. The one located beneath the brake booster, very hard to see and probably often over looked. I used a VW relay and rotated the center spade 90 degrees to fit the bimmer plug. Ha! Problem gone.
 
You must log in or register to reply here.
Back
Top