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  #61  
Old 01-25-2010, 02:12 PM
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Looking for a short can be maddening not doubt.

Id disconnect the battery and start checking each wire with an ohm meter to ground on the lowest scale you have. You should not get even a quiver on the meter is a line is good.

Quickest way to isolate the issue is at the fuse block. Pop each fuse up and check each side. If you get no zero reading (direct short) then you will have to come up a scale or two and repeat the test until you find the circuit that is giving you the problem as shown by getting a reading.

If the issue turns out to be a multiple connection cluster, pull them off and check each one. That procedure will at least get you to the right circuit that is giving you the problem. I would start on the power side of the fuse block rather than the item side.

You may just find its going to be easier to run a second wire to repair the bad one rather than trying to find the physical short and fixing that.

DVM's are super for working on vehicles as they are more than accurate for us, the are quite durable and best of all for a good working tool, they are cheeep. They are readily available on our favorite auction site for under $10 delivered.

I cant seem to post the same pic twice so here is a link showing the meter I am talking about. A good place to find a 12v Always live source

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  #62  
Old 01-26-2010, 08:29 AM
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One very simple test that should be done before you rack your brain trying to find a short, is to check the alternator with the engine and ignition off. I had a problem where a failed diode in the alternator caused a current drain via the alternator case to the engine block. All you have to do is disconnect the battery cable from the alternator post, touch it to the post again, and if you get a spark at that location, then that is your problem. Hope this helps
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  #63  
Old 01-26-2010, 10:09 AM
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Cold weather has literally killed my car every winter. I've gone through batteries every year until this year when I bought an Optima Red-Top and haven't had a problem with it yet. Only this year I had to have the starter rebuilt (from a morning of my dad trying to start it without it being plugged in overnight). I learned my lesson.. PLUG IT IN! Also, I've replaced the glow plugs and relay. Solved all my problems.
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  #64  
Old 01-26-2010, 10:50 PM
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Cool Don't pull the dash!!!

Alex/Jim,

I gutted all of the electrical components on Fuse #2 and mean everything. Dash gauge assembly (a *****), radio (yes its aftermarket but I installed it and know my wiring is right), A/c control unit, all switches on the dash and counsel, front and rear light, and still nothing but the damn 4 amps. My wife wanted to go to the market, saw the car and couldn't believe her eyes..... Her car was like what you would find in a junkyard, every thing stripped out. I just laughed and told her I was about to take it to it final resting place....with a smile of course.

I spent two days on this and wife is happy to see her baby back together. But still need to find this problem, "I won't be BEAT".

I am leaning towards the alternator leaking diode. It is possible that diodes can fail and allow voltage to reverse. If so this could be the path to the fuse box. I am just grabbing at straws for now and will try to run a test and let you know what I found out.
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  #65  
Old 01-27-2010, 07:15 AM
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normally diodes fail open circuit. You can just pull the plug on the back of the alt to disconnect it.
4 amps is a bit. Is the light in the trunk on?
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  #66  
Old 01-27-2010, 09:53 AM
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It may be the alternator. Pimpernell, do you mean disconnect the wire going to the alternator from the alternator itself and then reconnect? Wouldn't that show the same thing as unplugging the positive battery cable and touching it to the post?

Ricky, it's discouraging that after pulling everything you still can't find it. One thought came to me last night: does your aftermarket radio have a clock? If it does (and if it works), that means that there's live current going to it, to keep it accurate when the car is off, at all times, probably from one of the lines connected to fuse #2. I've read (in the link TNBob posted below) that to get a radio clock to work properly, you have to split the wire going to the original clock (which is live at all times) and connect it to the radio. Splitting it may cause it to draw more current than necessary. I'm going to pull my dash and see if this is the issue.

Also, it is no coincidence that fuse #2 is drawing current. Everything connected to this fuse is alive even with the ignition off (i.e., clock works, trunk light/interior lighting comes on, vanity mirrors, etc.). There is going to be a draw for this fuse no matter what, it just needs to be minimal. It almost feels to me that is HAS to be one of the accessories or a wire going to one of them. If it were the alternator, fuse #2 wouldn't be drawing current. The battery, on its own, would--is that safe to assume?

I hate my radio. I'm going to smash it with a sledge when I find a stock one to replace it with.
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  #67  
Old 01-27-2010, 09:53 AM
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Dead battery

I had a charging problem with my 85 300Sd took me 9 months to figure it out.What it was the glow plug relay was sticking in the on position would kill the battery even while driving it because the alt. could not overcome the draw.What helped me figure it out was I hooked up a simple voltmeter on my dash when at one point I saw it discharging I simply unpluged the GPR and presto it was charging like a champ.
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  #68  
Old 01-27-2010, 09:56 AM
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Quote:
Originally Posted by yuke View Post
I had a charging problem with my 85 300Sd took me 9 months to figure it out.What it was the glow plug relay was sticking in the on position would kill the battery even while driving it because the alt. could not overcome the draw.What helped me figure it out was I hooked up a simple voltmeter on my dash when at one point I saw it discharging I simply unpluged the GPR and presto it was charging like a champ.
I hear my glow-plug relay switch off after about 30 seconds. Also, the draw (for me and for Ricky) is coming from something connected to fuse #2. Don't think it's the glow-plug relay. But a dash voltmeter isn't a bad idea...
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  #69  
Old 01-27-2010, 10:13 AM
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You could use a test light to test for wires that have grounded out.
http://autorepair.about.com/od/troubleshooting/ss/TS-circuit-tstr_2.htm
  1. Disconnect the battery at the positive terminal.
  2. Clip the test light to the positive terminal-the pointy probe is now hot.
  3. You can use the probe to find ground- make sure it works by scratching through oxide on the engine block, chassis, ground strap, whatever, you should get a light indicating a complete circuit.
  4. Probe for ground where you suspect a current leak, by scratching through oxide on device terminals, or by poking it through the insulation on the hot wires throughout the car. A glowing light means you've found a grounded conductor. Be careful not to poke through your finger with the probe.
The wiring diagram for your car is in the shop manual on CD. It will show you what comes off of fuse #2, what it feeds, and where the devices are on the chassis. Alternatively, you could follow the grounded wire from the fuse #2 terminal and see where it leads you. At least in a 240D, the dash forest is more fearful in imagination than reality.

If you don't have a warm place to do this, you could make a lead with an on/off switch, in line fuse and alligator clips. Pull fuse #2 and clip your cheater lead to both terminals. Make sure that your switch and fuse are rated for the same current as fuse #2. Turn the car on, then turn the switch on. Turn the car off, turn the switch off.

Another alternative is supplying fuse #2 with power that is switched on by the ignition key. You'd have to find the relay that does it and take power off of the one of the switched terminals. I'd worry about overloading this relay, I don't know what margin this relay has.

With either cheat, you'll always lose your radio settings. BTW, can you listen to the radio without the keys in the ingnition?
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  #70  
Old 01-27-2010, 01:31 PM
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moon, as always, a lot of great info. I'll try tracking down the ground. I have a feeling I'm going to have to tear the dash apart so I hope you're right about it not being as bad as you would think. I don't want to draw power to fuse #2 from another line. I want the interior lights, clock, trunk light working without the ignition on.

Quote:
Originally Posted by moon161 View Post

With either cheat, you'll always lose your radio settings. BTW, can you listen to the radio without the keys in the ingnition?
Nope. No power to the radio with the ignition off. BUT, the radio display does light up and does display the time. I think to supply power for these, some wires somewhere were spliced (including the power supply to the clock). Would this cause the issue?
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  #71  
Old 01-27-2010, 03:39 PM
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Exclamation Disaster in Fuse #2

Alex/Moon and Others,

When I mentioned above about REMOVING ANY ELECTRICAL component possible I meant PHYSICALLY REMOVED, disconnected, set-aside, displaced, etc....
If everything is removed from this circuit there should be no load UNLESS this fuse terminal is powered through a relay that could be stuck (Note: Removing the Fuse #2 drops the amp to less than 1.5 draw). The glow plug relay is not powered from Fuse #2 and doubt this would cause this amp draw. I don't know what is next other than to just remove the fuse or disconnect the battery when not in use as Alex has for a long time until someone here has experienced this problem and solved it. It has been my experience that diagnosing electrical problems can become very time consuming. Almost always the usual fix can be very simple once known. It's just getting to that point.

I appreciate and value everyone's input. It has actually given me other ideas that may help in solving this mystery.

As a footnote; the dash clock does not pull more than .05 MA. Alex, I wouldn't expect you to still measure the 4 amp draw you stated above. When I removed the dash as mentioned above the drop was only .15+ MA. Guaranteed this isn't the source.

LAYBACK40 mentioned the interior lights;
I have a back interior light that has two functions. 1. When any door is opened this light is energized, a timed relay located in the front interior light component. 2. Back interior light can be energized by switching from Auto to On.
What I found is that this light didn't work at all. In making a few tests I found that when the tailgate was open, pushed the tailgate release button the light energized. What even more disturbing is that when I open the door the light turned off. By closing the door the light turned on.

I may have a short in the tailgate locking mechanism. I am going to research this today. If anyone has had this problem before I would like your input.
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  #72  
Old 02-07-2010, 05:34 PM
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Solved.

So I found the draw. It was the aftermarket radio like I had suspected. I pulled the entire dash and all the wires then put them all back. There were two wires that were just sitting back there, loose, not connected to anything (maybe for the electric antenna that's been bypassed, which is also connected to fuse #2). I taped them up, put the whole thing back together and now I'm getting a .01 - .02 amp draw at the battery terminal. I'm guessing this is normal - does everyone else's have this much draw with the car off and the key out (guess it's the clock)?

Ricky, did you figure out where your issue was?
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  #73  
Old 02-07-2010, 06:23 PM
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Quote:
Originally Posted by AlexHart View Post
I'm getting a .01 - .02 amp draw at the battery terminal. I'm guessing this is normal - does everyone else's have this much draw with the car off and the key out (guess it's the clock)?
Normal draw. Anything below .06 amps is fine.
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  #74  
Old 02-07-2010, 06:56 PM
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Thanks for confirming, Brian. Feels good to have solved this. Thanks for everyone's help. It is truly appreciated.
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1984 300CD - Silver/Blue - 326,000 miles (sold)
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  #75  
Old 03-30-2010, 01:14 PM
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Still an issue Alex

Quote:
Originally Posted by AlexHart View Post
So I found the draw. It was the aftermarket radio like I had suspected. I pulled the entire dash and all the wires then put them all back. There were two wires that were just sitting back there, loose, not connected to anything (maybe for the electric antenna that's been bypassed, which is also connected to fuse #2). I taped them up, put the whole thing back together and now I'm getting a .01 - .02 amp draw at the battery terminal. I'm guessing this is normal - does everyone else's have this much draw with the car off and the key out (guess it's the clock)?

Ricky, did you figure out where your issue was?
I checked for other wires that may have been discarded when the new radio was installed and found all were accounted for. As for the antenna, no bypass suspected. Hmmmmm....

Glad you found your problem Alex... I am still looking for other ideas.

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