The Draw from Hell! 1986 Mercedes-Benz 420 SEL - Auto-Trend Repairs and Service Information Forums

SELLC · CERTIFIED POST WHORE

The Draw from Hell! 1986 Mercedes-Benz 420 SEL

SELLC · CERTIFIED POST WHORE

RE: The Draw from Hell!

PowerStroker · UNSTOPPABLE!

SELLC wrote:

Problem I am having is this sucker has a killer 12V draw.

Voltage is electrical pressure, Amperage is electrical flow. Parasitic drain is measured in AMPS. anything less than 50 milliamps is considered normal. Often it can take up to 45 minutes for all systems to shut down before an accurate reading can be measured... anything that disturbs the electrical system ie: opening a door to pull fuses can wake up a body control module by activating the dome lamp (even after the 45 min timeout), and cause you to need to start all over from the beginning.

1 key off and removed from ignition.
2 open drivers door and hood - latch any door/hood ajar switches.
3 hook up ammeter in series with battery and wait 45 min.
4 If reading is above spec, pull fuses 1 at a time until reading falls below 50 milliamps.
5 reinstall affected fuse and disconnect all branch circuits fed by that fuse one at a time until the meter reads less than 50 milliamps.
6 If you read 0.0 milliamps on your meter it's because you are set to the wrong range, or worse - did a bonehead move and blew the internal ammeter fuse, if this happens - you FAIL the course. If you need to ask the instructor for another ammeter fuse you will be expelled from the brotherhood of marginally worthy Mafia whipping boys.
7 if the parasitic draw never falls into spec no matter what fuse is pulled, then it is happening somewhere that isn't fused ie: the aforementioned aftermarket bullshit, or possibly the starter ckt or other non fused path.
8 if the meter reading is in spec but it is obviously drawing more than the meter shows - corrosion on top of the battery can cause negatively charged valence electrons to reach the positive plate via the corrosion path - thus bypassing the series wired ammeter.

I'd eliminate the aftermarket bullshit first just because it sucks and is probably your problem.

None of this is a PowerStroke specific concern so I'm not afraid any of this advise will sell out any Mafia trade secrets.

-- Edited by PowerStroker on Saturday 28th of March 2009 03:44:56 AM

SELLC · CERTIFIED POST WHORE

Unlike the newer Fords, these old Mercedes do not have a relay that cuts power to accessories after a certian period of time.

Also unlike the Ford, the Mercedes has quality pin swiches for the door switch, not ones that are enclosed into the latch mechanisim that require substantial work/money to remove and replace. Just sqeeze two clips and its out.

I have already removed ALL relays, fuses and no such luck on killing the draw. I have also removed the fuses from the aftermarket systems with no luck there.

I did find one of the main power wires that runs into the dash that will cut the draw, however it also knocks out just about everything in the cabin. What a nightmare. These vehicles have many relays, and there is a good chance that one of them is being effected, causing a back feed into other systems, as there are some weird quarks every since the install of aftermarket systems. Sometimes you will hear a bunch of clicking behind the dash, the re-circulation light will flash, and it would even cause the vehicle to stall. Thats when I told him to take it back to the place that installed the stereo (this was last year) needless to say the asshole installers could not figure it out. So here it is again.

PogoPossum · RIP - Veteran User

Like Powerstroker, most of the world measures parasitic draw in milli-amperes... If you are getting a reading of 12V, you are doing something wrong.

Old Mercedes Benz are bound by nature and the laws of physics to obey the same rules of electricity that Ford (and all the rest) must observe.

Electrical diagnosis, believe it or not, is much simpler than many imagine it. Once we have a firm grasp on Kirchoffs Law, we can analyse and diagnose a base electrical concern quite easily.

To add salt to the wound, a trained tech should never be surprised at the butchery aftermarket accessory shops are capable of. Scotchlock connectors in place of soldered, heat shrinked connections.... Poorly selected, poorly placed or missing circuit protection... The list is nearly endless....

And THAT is what bargain hunting gets you.....

SELLC · CERTIFIED POST WHORE

I just love it how these guys want to talk about milli-amperes when there is a direct 12 Volt draw.

Were not talking about a little draw here, were talking about a full on 12V draw that illuminates the test light. I have been able to eleminate the circut to cut off the draw, however I am still working to figure out what componet is doing it.

I understand that in some cases you would want to measure in milli-amperes, when the draw is rather small and barley illuminates a test light, however in this case its pretty obvious. But thanks for the support, even if you were just trying to get in some digs.

SELLC · CERTIFIED POST WHORE

PogoPossum wrote:
Like Powerstroker, most of the world measures parasitic draw in milli-amperes... If you are getting a reading of 12V, you are doing something wrong.

I understand in cases where there is a "SLOW" draw, one would want to break out the amp meter to get a bearing of just how much load is being put on the system, however in this case the draw was quite large and killed the battery overnight. Given the brightness of the test light its clear to see its drawing some major amps. A weak draw, or the kind of draw thats acceptable (THE KIND THAT SHOULD BE MEASURED IN MILLI-AMPERES) will be tested once the major draw has been eleminated. Using the test light makes monitoring the draw while pulling fuses MUCH EASIER. I dont expect you to know this since you spend all your time in a book, rather than under the hood. - SELLC

Old Mercedes Benz are bound by nature and the laws of physics to obey the same rules of electricity that Ford (and all the rest) must observe.

Sure they are, however most techs use a test light to isolate a draw, and dont act like they dont. Spend more time fixing them than reading about them and you will know. - SELLC

God, look what you made me do... You made me pull a FordGirl! Werent you the guy whom turned away a Mercedes because it scared you so much, that you claimed it darkened your doorstep? LOL

This area is not for the weak of heart. Feelings get hurt in here, and they sure as heck aint mine.

SELLC · CERTIFIED POST WHORE

Well the problems got fixed.

As I thought, the aftermaket Avatel alarm system was back feeding into the system, causing engine control relays act up. Un-hooking the aftermaket alarm was the solution for the stalling.

The draw was a little diffrent and resulted in us having to switch the circut to a "Key On Power" source, rather than constant power. I am unaware if this was done by the install shop, however we spent a lot of timing tracing down the draw. It was coming from the constant power side of the factory installed Mercedes alarm. Likley because the module was missing. The aftermaket installers butched up the systems pretty bad. In the end switching the power source was much less expensive than having us rewire the entire system.

It is amazing just how much the factory alarm system is tied into. Almost all the exterior lights, door switches, ignition, trunk and hood switches, stereo and many other systems are involved. For reffrence the Alarm system module is located on the passengers side foot well under the floor mat. The module is made by Becker and almost appears to be a stereo module. Make no mistake, its really the Alarm system module.

Rastus · UNSTOPPABLE!

RE: The Draw from Hell! 1986 Mercedes-Benz 420 SEL