Searching for a voltage drain, need help interpreting results... - PeachParts Mercedes-Benz Forum

Rahulio1989300E · #1 03-03-2010, 05:30 PM

Hello,

I just got a Craftsman 82139 Autoranging Multimeter specifically for testing for a suspected voltage drain and to make sure the duty cycle was in the desired range.

My battery seems to get quite weak if the car is left untouched for any period longer than 5 days and appears to be almost flat if left for about 10 days.

I tested fuse terminals A and 1 in the fuse box near the drivers door and got a reading of:
Terminal A: 0 A
Terminal 1: 0 A

Just to be sure I switched the meter to mA and tested both again:
Terminal A: 0 mA
Terminal 1: 0 mA

So far so good, so then I skipped to the two terminals I suspected the most. Terminal C and Terminal 9.

Terminal C: rear roof light, trunk light, rear door locking system, safety belt handover arm, seat back arrester, central locking system, door lights, reading lamps, aut. antenna, control seat adjustment.

Terminal 9: clock, radio, some other things (forgot to write it down)

I am pretty much new to this kind of test procedure, its my first multimeter.
My results are confusing to me, could anybody clarify? I tested both Amps and milliAmps.

Terminal C: 1.24 A
Terminal C: 1.21 mA

Terminal 9: 2.57 A
Terminal 9: 2.62 mA

I have no idea why it is giving me these readings, if in fact the car is drawing 1.24AMPS at Terminal C, wouldn't the muiltimeter tell me the reading is out of range when I try to read the terminal using the MILLIAMP setting? Or is the dot on the LCD in the mA mode supposed to be a comma?

This probably has a very simple answer, I am an idiot when it comes to multimeters:...

This is for the 300E.

Rahulio1989300E · #2 03-03-2010, 05:45 PM

I just flipped through the manual and realized that I am supposed to switch the red lead to the left most connection labeled 10A... I really am an idiot... going out to retest...

Rahulio1989300E · #3 03-03-2010, 07:29 PM

Found the voltage drain!

It was the trunk light, for some reason, the light is no longer turning off after I close the trunk, I tested the amperage draw again and it was found to be 0.70 Amps. It is enough to drain the battery within 10 days. I have removed the bulb for now and the draw has been eliminated!

Chalk up another one for the maniac!

400Eric · #4 03-04-2010, 05:28 AM

Thanks for posting! This may help me with my 89! M-103: too many issues for the title...
Regards, Eric

400Eric · #5 03-11-2010, 11:39 PM

Quote:

Originally Posted by Rahulio1989300E

Found the voltage drain!

It was the trunk light, for some reason, the light is no longer turning off after I close the trunk, I tested the amperage draw again and it was found to be 0.70 Amps. It is enough to drain the battery within 10 days. I have removed the bulb for now and the draw has been eliminated!

Chalk up another one for the maniac!

Turns out this is the situation with my car as well. Do you or anyone else happen to know where the switch is that controls the light? Normally I would just remove the light too but since I have to go to the U-Pull-It anyway, I thought I would pick this switch up too but I can't figure out where it is. After I fix this, I'm gonna update my thread too!
Regards, Eric

compress ignite · #6 03-12-2010, 07:08 PM

Look underneath it...
White plastic "Push-Button" switch sticking down Vertically...
Wires run through the Hinge Arm.

Mark your Trunk Lid Lock Plate Orientation before removing(If Necessary).
[I just mark mine,and loosen the two bolts enough to slide the "Felt-ish Liner" out.]
[You don't want to have the plate the two bolts screw into slide AWAY!]
[the "Liner" has got the plastic "Push Pins" securing it on the sides.]

I might also suggest inspecting and testing the Switch Wiring for Continuity...
it is subject to Flex strain at the Trunk Hinge point underneath the "Hat Rack".
(Just like the Wiring in the "B" Pillar to Rear Door AND "A" Pillar to Front Door)

400Eric · #7 03-13-2010, 04:37 AM

Thank you very much! And to think the whole time I was looking for that pin it was literally right above my head! The fact I was searching in the dark doesn't help any. I was doing all this in the dark because that made it easier to see if the trunk light was staying on when the trunk was closed. Thanks again!
Regards, Eric

400Eric · #8 03-14-2010, 01:42 AM

I had removed the back panel inside the trunk to gain access to the vacuum unit that locks/unlocks the trunk so I could find a leak I could hear but not see. I had been having trouble with the locking system because of that leak. It turned out the unit itself was bad so I left everything apart till I could get a replacement unit at the U-Pull-It. I did plug the air line so the rest of the system could work properly once again. Unbelievably, the pin that controls the trunk light lines up with one of the pins that holds the back panel in place. Panel pin missing = trunk light pin not being put into the "closed" position when the trunk is closed. I now have two business cards wedged into that area which has solved the problem! No more current draw! (Actually, it's .02 to .03 now and with the clock's fuse removed it goes down to .01).

I have already obtained another locking unit..... just have to install it now.
Regards, Eric