Battery Drain - PeachParts Mercedes-Benz Forum

john2031 · #1 01-05-2008, 04:26 PM

I have a 1990 300SEL. I purchased the car knowing that something was draining the battery. Circuit #2 is drawing more amps than my meter can measure. I removed the fuse and the battery stays charged. This circuit controls the following: clock, radio, hazzard warning, vanity lights, electric illumination. I unplugged the clock, radio, hazzard relay, vanity lights and measured the draw and it is still to large for me to measure. By large I mean that the meter just shows 1. If I could tell which item is causing the problem I might could solve it. Do the things on this circuit have individual wires under the fuse box that connect to fuse #2 or is there 1 wire leading from the fuse box that brances off to each curcuit? The antena is unplugged also because I know they can cause problems. Any help would be appreciated!

RKreutzer · #2 01-05-2008, 07:50 PM

Hi there,
I might not be of much help, but based on your description, only the electric ilumination seems to be left, if you have disconnected everything else properly. Was there anything not working like the hazard switch or the vanity light with #2 in? That might give a hint where to search. After that, you have to follow the wires and look for any broken insulation and test the switches etc. Somewhere is a short to ground that you need to find. The voltmeter has to work also.
Good luck

john2031 · #3 01-05-2008, 08:36 PM

With the fuse in #2 everything works. The battery will be dead within 2 days. It seems as though the fuse would blow because it is only 8 amp. I hate driving without a radio.

Gilly · #4 01-05-2008, 09:25 PM

There are individual wires attached to the fused side of the individual fuses, but they are not marked and in many cases the wires are even the same color. The wires attach with a phillips-head screw. You could definitely pull all the wires off and start attaching them one by one until you find the power hog, then just leave that one off and find out what isn't working anymore. 126 fuseboxes are nice to work on, lot's of room to work.

Gilly

john2031 · #5 01-05-2008, 09:55 PM

Thanks for the information. I will take the wires off one at a time soon.

john2031 · #6 01-07-2008, 04:07 PM

Gilly,
How do I get to the wires for each fuse? It looks like an individual cap for every 3 fuses. I tried to open it but it would not open. I did not want to break anything.

cummins · #7 01-11-2008, 12:03 AM

You could unplug one item on that circuit at a time and see which one stops drawing voltage and/or amperage

john2031 · #8 01-11-2008, 04:16 PM

I unplugged the clock, radio, hazzard relay, vanity lights and measured the draw and it is still to large for me to measure. The only thing I haven't unplugged is listed as "elect illumin" on the fuse box card. I don't know what this is.

bhatt · #9 01-11-2008, 05:32 PM

What "amps" do you mean? Is it an aftermarket radio with amplifiers?

Try these suggestions, one step at a time to identify the drain:
-Pull the "main" fuse in the amp wire. It should be located close to the battery. Should be an inline fuse if it's an aftermarket amp.
-Check the amps for a blade-style fuse and pull each one separately (if more than one amp) to see which amp is causing the problem
-Pull the radio and remove the two fuses (one for constant power, one for ignition power) and see what happens.

You have something killing your battery, and it sounds related to the radio. Disconnect all of the radio stuff until the drain goes away, then start adding back one thing at a time until you find the problem. No need to use your meter as you've narrowed it down quite a bit.

Easiest way is to just stop the drain, and then slowly (wait a few days each time) add one thing back till you find the offender!

RKreutzer · #10 01-11-2008, 06:06 PM

Hi again,

I can feel your frustration. Shorts are sometimes hard to find.
Electric illumination is the lighting behind the instrument panel, the dimmer to regulate the instrument lights etc.

I looked at my Hayes electrical manual and it stated that a drain of .5 amps is probably excessive and will drain a battery.
Now you know already the fuse, that is suspect.
I would want to have an instrument that can read that drain in that general magnitude. So setting my multimeter to mA should give me something like 500 or more on the scale, i.e. 500mA = .5A. I don't think uA is the right setting.
I connect my multimeter between the negative battery cable and the negative battery pole and see what I read. You need to read something at that spot that makes sense to you like more than 500 mA.
Now I remove the fuse and that number should be close to Zero.
Then you proceed as Gilly has suggested, i.e disconnect all at the powerside of the fuse box and put them back on one at a time and measure their power draw. Again, it should be in the mAs and one of them should stand out and being close to the total draw measured at the beginning.
As Gilly said, that one you leave off, start the car and see what is not working. Then you follow that circuit.

If the drain stops when you disconnect that fuse, it has to be on that circuit.
Good luck

john2031 · #11 01-11-2008, 09:03 PM

I have a Greenlee DM-20 Meter. The settings for amps are 2000u, 20m, 200m. I have not checked the draw at the battery terminals but will do it tomorrow. There are 2 spades on the powerside of the fusebox with 4 wires each so it is not possible to pull them off one at a time. I checked each spade and they both were pulling too many apms. As for the radio it was the original one, but had 2 small amplifiers, one on each side of the rear seat. I replaced it with a radio/CD with a built in amplifier. I removed the old amplifiers and bypassed the fader switch. Accoriding to the wiring diagram for the instrument cluster/console lignting fuse #2 is hot all the time and connects to N4D Instrument Illumination Control Unit. All the lights in my cluster work but 1. I don't know what the N4D Control unit is for. Whatever it controls should not work with the fuse removed. Thanks for all the help.