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  #1  
Old 11-22-2006, 10:07 PM
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Question W123 electrical -

Hello and Happy Thanksgiving!

I have gone through the archives and gleaned alot of good info.

Until my car battery recharges, I am submitting these questions for extra tips.
1979 300D. 163K miles. Garage kept. No water/rain interaction this past week.
When running, a multimeter reading shows 13.8 volts at the battery terminals with engine at higher than idle revs.
Seems like alternator is good. Archives confirm 13.8 volts as adequate. (Alternator is a Bosch 005-154-98-02 88 remanufactured replaced June 1995 at 110,825 miles).

I replaced the battery on Sept. 19 2006 with an appropriate Interstate battery. The old one lasted about 7 yrs. So battery is new.

Yesterday my car's battery was very low. (11. volts.approx)It had enough juice to keep the clock working and interior lights. Car would not turn over at all though. I jumped it and the car started easily but I shut it off after 2 minutes because I had no time to do a freeway run .

I also made sure that I turned off the radio properly thinking that I may have accidentally activated a stanby mode which may have drained the battery since last used 2 days previous.
Tested the trunk switch and light. It works and bulb was not hot to indicate it had stayed on.

~Discovered glove box light did not work. Removed the bulb and the bulb filament looks whole but untested yet. Yet to remove the glove light switch to inspect. Forgot to look at cig lighter.

Both front and rear interior lights work but the switch that activates the rear int. light does not activate the light. Other accessories on that dash panel not tested at that time.

Used contact cleaner on the alternator connections and general area.

Today I tried to jump start. Did not start. Battery read about 2.3 V with multimeter before jump.
After leaving jumper cables on for over 5 minutes with other car at fast idle, still could not start the 300D. Not enough juice to activate starter. Seemd to want to go.
I tested battery with jumpers off. Tested around 11.7 V (as a result of recent boost). After about 20 minutes it went to about 2.3 V

~ I noticed that when I took a multimeter reading of the battery terminals intact with battery cables, the reading was about 2.3V
When I removed the neg. battery cable and placed the meter terminals onto the battery terminals (pos terminal still connected to pos cable) the reading was about 6.8 or 5.8V. It went up.

~~So, is this normal that the negative cable will cause a lower reading of the battery?

I inspected the battery cables as best as possible. No visible evidence of bad.

I could not yet locate the ground wire from engine block to chassis.
~~Where is it?

~~ I read that the grounding of the alternator should be checked. Where is that?

As soon as the battery recharges- it is on a charger... slow... I will do the ammeter on series and individual fuse tests as per archives.

I already remioved the glove box light/radio fuse today. just to remember that this may be one source of a leak.

Also could the alternator brushes still be suspect?? If so how to know if my alt. has the replacable ones?

By the way, the battery cables were clean and tight previous to any dinking around after the fact.

Any insights at this point or tips, opinions???
When last running, all basic functions seemed to work.

Thanks

Denis
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1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Last edited by unkl300d; 11-22-2006 at 10:16 PM.
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  #2  
Old 11-22-2006, 11:02 PM
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I'll post just to bump your problem up again.

Definitely agree that an ammeter will help - sure sounds like a voltage drain/draw to me. I believe, although am far from an electical expert, that this is what explains pulling your neg. cable and having an increase in voltage. While the neg. cable is connected, you're completing the circuit and the draw is being made.

I like your approach to solving this - one of the 'experts' will need to chime in to help however....

Try not to let your battery drain down so low while troubleshooting.
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  #3  
Old 11-22-2006, 11:02 PM
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Pull your clock fuse. Put your meter in the line of the battery circuit. Between the negative terminal and cable is fine. Keep pulling fuses till you get a zero reading. Then you have no drain at all. If it does not do it by pulling fuses disconnect the alternator. You might have a shorted or leaky diode in there. I have run across a few cases of aftermarket sterios draining the battery when off as well. Kind of sounds like you have a pretty heavy drain.
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Old 11-22-2006, 11:30 PM
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Could also be the glow plugs draining down the battery thru a faulty glow plug relay. This is probably the highest draw on a sleeping car except for an accidental short thru a frayed wire, and can really dump a battery in short order!
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  #5  
Old 11-23-2006, 05:54 PM
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Thanks all.

Update, I had the battery on a charger overnight.

It measured 12.3-4 in the morning.

I did the systematic ammeter in series. Initial reading was 2-3 mA
Pulled all fuses methodically. No drops at all. Same 2-3 mA reading with all fuses out.
Retested radio/glove box fuse and it still did not waver the ammeter.

I checked the voltage drop between the alternator case and the neg battery post. This was zero.
I did not yet check the V drop of alt. pos connection and pos battery post.

Started the car up and drove it 30 min. on freeway. Back home I tested the charging at high idle and it read (edited)13.6-13.7V.
Once the car was shut off I tested battery voltage at posts with cables connected and it read 12.47 V
~This time the voltage difference between testing with neg cable on and off did not produce such a dramatic drop. Very minor drop. Perhaps my first such test yesterday was dramatic because the battery was very low. In the second test the battery was charged up 12.3-4V

So, I shall retest tomorrow and see whether the battery goes low again.
If so, more tests to be made.

__________________
1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Last edited by unkl300d; 11-24-2006 at 12:38 AM.
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  #6  
Old 11-23-2006, 06:55 PM
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If after your highway run you had no load like lights on etc. I am not sure with mercedes alternator at high idle you should have been that low in voltage. You could check the archives for what is standard on them. Or check the voltage across the battery at high idle with the lights on. I still feel you should see 13+ volts. If you do not pull idle up 1 k with lights on and read again. It should be 13+ in my opinion. I might go over the grounds in the engine compartment. Especailly if the archives indicate you should have more. I realise that you did the alternator case to negative terminal voltage test to see if You had a bad or marginal ground. You might have found the basis of your problem. An under charging alternator might be a possibility. If so you will find it now. The possibiliy of a load when car is off off you seem to have eliminated pretty well. Something brought that battery down. Or run with your headlights on and see if battery holds the 12.47 volts with everything off. If not of course the alternator is not keeping up with the load.
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Old 11-24-2006, 12:41 AM
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Barry I made a typo error and corrected it above. Should have read 13.6-7 V reading. Yeah 12.6 would be way low. Two days ago it read 13.8 so it ought to be OK.
At 12:45 PM today the battery read about 12.47V after the freeway ride. Just now, 8:40PM, the battery read 12.08 both readings with the car off.

I'll see tomorrow if the car starts.

Cheers.
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1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD
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  #8  
Old 11-24-2006, 01:58 AM
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A good battery should not drop from 12.47 to 12.08 Volts in just 8 hours. Further, a new battery should 'float' after charging at more than 12.5 Volts.

If the "switch off" drain on the system is really only a few milliamps, as you have indicated, the battery should not drop down so much so fast. A few milliamps is normal for most cars; the current is drawn by the clock and various always-on electronic circuits.

An additional test would be to charge the battery with the negative car cable disconnected. Then measure the float voltage of the battery and let it sit for 8 hours, 24 hours, however long you can stand to wait. If the battery voltage won't stay up with no load at all then you have an internal short. This is unusual in a new battery but not impossible. Definitely a warranty situation.

Let us know what you learn.

Jeremy
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  #9  
Old 11-24-2006, 09:55 AM
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oh, and 12.4 is not a fully charged battery.
fully charged is near 12.75 higher readings will occur immediately after charging.
if your battery only reads 12.4 after a full night of charging with everything disconnected, you have probably killed the battery. when a LA battery goes below 8 volts, it is pretty hard to get them back to full charge again. interstate has great warranties, return the battery, charge the new one overnight on trickle charge, and retest everything.
I second the GP relay draw. I have left my lights on overnight, and still had 12 v in the morning. theese batteries have amazing capabilities. my guess is you got one that had been discharged already, and you hooked up with a bad GP relay.
John
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  #10  
Old 11-24-2006, 01:50 PM
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After the freeway drive dropped to 12.08? Something is going on as you are all too aware. The glow relay may be hanging up or coming on and dropping out intermittently. It is easy to disconnect after starting to see if things return to normal. You may yet be forced to wire a cigarette lighter socket to your meter to monitor the battery voltage and how that alternator is producing with the meter on your seat. If the drive home was with no headlights then the glow relay does become a prime suspect. If not the relay then the battery was not seeing the 13.5 + alternator output. Nothing in the car has a draw strong enough to overcome the alternator except that and the starter. The starter is eliminated of course automatically. I would monitor while driving now. Some of your voltage postings might indicate the battery is not really fully charged. Or perhaps almost overcharged with a bad cell. I think 12.56 is considered a full battery but not sure. Make sure to carry a set of booster cables in the trunk with a spare battery if possible till you locate this. I have a feeling you might need them. Make sure to have mercedes free roadside assistance phone number with you if you do not have a spare battery. Sometimes it's on the back of the glovebox door. Not an earth shattering problem but just a pain in the posterior.
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  #11  
Old 11-24-2006, 03:21 PM
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Hello all. Very useful opinions and tips. Thank You.

This morning at 10:20 AM the battery in the car read 11.8 V . The first attempt to start car was 80% almost success. After the second attempt (which was not as good.) the battery read 11.60 V.

The battery charger I am using is a puny 1 AMP model and the instruction book actually states that it can take up to 40 hours to charge a 12V battery fully.
So, the battery may not have been peak charged but it started the car with ease yesterday and after running on the freeway (with lights off and acc. off) I figured the ALT would charge the rest. But alas this morning the battery has drained to 11.08V

So, the battery is on the charger again and I am doing some more inspecting of observable connections.

I had always charged the battery with both cables disconnected. Thus it is now on the charger.
I will follow some tests indicated by you all and also contact the battery seller to see about a 'load test' and possible battery replacement.
I don't rule out the GP relay being sticky or something else.

Up to now, there definitely seems to be a drain from somewhere most certainly.

more later. More tips welcome. Thanks.
__________________
1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD
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Old 11-24-2006, 08:22 PM
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Well, I just got WheelWorks (battery dealer) to check the electrical system
and I did further analysis.


~Prior to going to the dealer, I jump started the car and drove hiway for 20 minutes and the reat of the 20 minutes was street driving and car idling while I waited to be attended.


3PM 24-Nov-06
Wheelworks used a medium-large sized hand held digital apparatus to first check the battery voltage and cranking power with car off. He said battery was marginal. I asked if battery had an internal short, he said he could not tell (later I reasked after he did the load test and he said the meter showed no int. short. He did seem to understand better that time...). He said its cranking power of 8 amps (?) was not up to par. Basically he assured me that once it charged up, it would be good. So far no premise for new battery under warranty.

To my surprise, the car started up for the rest of the tests.

He checked the charging system without load it was 13.74 V , with load (lights on and air blower on-not AC) it read 13.45V.
(remember the car had been running 40 minutes prior to test in order to catch any faults with a hot system).

He tested the alternator and starter by way of the apparatus and claimed they were good, no shorts etc.

Back home with car still idling I did some more checks with my Fluke multimeter.

3:25 PM

At idle, 13.73V alt. charging.
At high idle the meter read up to 13.94V

With the car off and battery cables still on, the battery at rest read 12.55V immediately after shutting car off.

Three minutes later after taking the cables off the battery posts read 12.48V
with cables quicky pressed on I got 12.48V-- no difference.

After another 4 minutes at 3:34PM battery w/o cables read 12.45V
At 3:35PM it read 12.44V
At 3:39PM it read 12.43V
At 3:43PM it read 12.42V

I stopped here. I will get a reading a few hours later to see if it drops significantly before attaching the 1 Amp battery charger overnight.


The other tests I made prior to shutting the car off were:

All external lights work. No burnt bulbs. Trunk light OK switch works.

The main trunk light read 12.96V across the bulb with car running.
The two horizontal lights on the trunk end-lip (safety lights for when lid is up at night) read -0.047V across the bare terminals each.
With headlamps on, these terminals read 12.38V
(I removed the bulbs to these lid lamps because they looked dark but filaments were whole. Did not test bulbs but remain uninstalled)

Glove box light terminals with car idling, read 13.57V (is this high?)
With the glove box light switch depressed the mater read 0.008V across the terminals.

~~~~~~~~~ Question so far, does a standing battery that is marginal , lose volts soon after the car is shut off or should it float within a certain margin of volts?

I plan to check the reading after a few hours to see how much more it drops if any.

EDITED-- At 6:45PM the battery read 12.32V A 0.10V drop in three hours.

A fully charged battery is supposed to float at some said volts. What is the margin of voltage loss just standing without cables attached??

Thank You.

Denis
__________________
1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Last edited by unkl300d; 11-25-2006 at 12:38 PM.
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  #13  
Old 11-24-2006, 10:57 PM
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I have a junky extra set of leads that I use to check each cell in a battery if I think the charge is of questionable condition. The leads are dipped into the electrolyte to get a voltage for each cell, as a bad cell or two is usually the failure mode for a battery. This eliminates the guessing about what is happening as the voltage drops after an in car run or a recharge from an external charger.

An other option is to use a copper nail as the dipped element with a set of leads that have spring clamps at the end. Actually a plain nail will work, as you are only needing relative voltages cell to cell.
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  #14  
Old 11-25-2006, 11:26 AM
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Slow drains

I've had two battery drainers lately.

#1 glow plug relay was on while running. 12.8 volt reading while running, but only lasted for about 100 miles then died.

Automatic antenna was broken and it stil thought it was on duty ready to run. So it was draining power while the engine was off. As I recall it was fuse #12 on a 1982 300 D.

Hope it helps
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Old 11-25-2006, 12:44 PM
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After the last reading last night I put the battery back on the charger. Today I will visit a friend who has a battery charger cabable of detecting problems etc. Then I may just go to another wheelworks and request a new battery..... but keep in mind that I may still have an issue somewhere....

Thanks

(edited) Back from friends place. Battery seems to test good.
Alternator keeps testing good.
Detailed car outside. Looks great!

In eve. on way home, heater does not work but blower does. Blower had been tested before but not an opportunity to check heat.

Next: check climate control amp and also Klima servo body and wires.

Battery is fully charged now and is garaged without cables attached to test standing potential of battery.
__________________
1979 300D 199 K miles
1995 C280 95 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Last edited by unkl300d; 11-26-2006 at 02:10 AM.
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