Its an epic saga to be sure... one that has, at times, been a white-knuckled pride-swallowing siege and endless source of emotional distress. The alternator is new, I put it in yesterday. Im getting a charge at the battery of 13.2-13.3 volts when the engine is running. When I put a load on the battery, ie. heater fan, lights, ect... its ok and doesn't really lose anything. The battery does not hold a charge longer than 5-10 hours. i have replaced the fuel pump, starter and solenoid, ignition wires, distributer cap, rotor (not in relation to this issue),... Ive, disconnected and cleaned all the wiring i can effectively get to, (battery lines, alternator, grounds off the block). the pattern is this... I jump it, it runs fine, however if I leave it alone (parked) for too long it doesn't have the juice to turn over. Now, something MUST be sucking juice from the battery, Ive removed more trivial fuses (not associated with the engine) in an effort to isolate a suspect... It occured again... dead battery. Im awfully certain that my battery is ok, and that the alternator is obviously charging the battery b/c after running the car, i turn it off and check the voltage- 12V. Ive checked the fusebox with the car off looking for abnormal spikes or "dim" readings on the voltage meter indicating a short or faulty switch perhaps. What would take THAT much juice from a battery in that amount of time and does it sound like the battery is not recieving enough from the alternator during idle? even if that were the case, it would not go from being able to turn the engine over immediately after running for a half hour to not in the span of 5 hours, n'est pas?

13.3 sounds low. I'm pretty sure (from what I remember) that I was getting 14.5 VDC after I changed the brushes in my alt.

Take the following four measurements (VDC) while running idle:
1. positive probe on the large post on the alt, negitive probe on the alt case
2. pos probe small post alt, neg probe alt case
3. pos probe alt case, neg probe battery negitive terminal
4. pos probe battery +, neg probe battery -

If you reply with these voltages I can help you narrow down the source of the problem (brushes, no excite voltage, bad ground, bad brushes).

Does the battery light come on before you start the car (key position 2)?

I greatly appreciate your assistance. Ive done what you told and here is the grand total:
I jumped the car, it kicked right over... aside from low power(start) it idles fine.
VDC (+) large batt. post on alternator (-) Alt. case = 14.30- 14.31V
VDC (+) small post off of alternator (-) alt case = 14.47-14.48V
VDC (+) alt. case (-) negative battery terminal = -0.03V Flat
VDC Battery 14.25V.
When I drove the car around the block after jumping, and shut it off. It again needed to be jumped. I did so and took these readings. The plot thickens, it rained last night and Im susipcious that something got wet... dunno. If i put a charged battery in the car and it does not even turn (as if it needs power) then Im thinking that the solenoid is emotional. This is not on topic and i apoligize, anyhow, no doubt that it drains juice off of the battery when not running. My next step is to measure the drain off of neg terminal and start pulling fuses to attempt to isolate. Again, ANY assistance is GREATLY appreciated. Happy motoring to all and have a great weekend.

also, yes the batt light does come on in key position two.

It looks like the alt is charging and you have good connections back to the battery. I'm wondering if you have an issue with the stater going bad and being the source of the current draw. Or maybe the ignition switch isn't turning off one of the circuits - hard to tell.

Agreed, next step is to take an in-series current measurement off the battery and start un-hooking things, one at a time ...

Hi

I had a similar problem with my '87 240. After a couple of batteries and an alternator based on my own guesses, my mechanic told me to measure the voltage loss when the ignition and all accessories are turned off by unhooking the positive battery lead and putting the meter between the post and lead. There should be a regular 'tick' for the dash clock. There may also be a very small draw if you have a radio/cd player with a clock. He said anything more is very likely to be a short somewhere in your power door lock system. I can't remember how big the draw was or where I disconnected the power lock system, but it solved the problem -- I didn't have time to track down the actual short but you get used to no power locks very fast.

Hi, this post is intended for Robert240, so, sorry for intruding, but I'm having a similar problem, so I did what you told him to do, and my Battery read 12.20 and every test on the Alt. like you said to do, nothing registered past 0.something except for when I put the Negative probe to the Alt. case and the Positive probe to the Pos. Battery terminal, that registered at a little less than just testing the battery alone, like 11. 93. Also I did the simple Alt. test of disconnecting the Neg. Batt. cable while the car is running and if the Alt. is good, the car should keep running, but my car died instantly. So obviously it seems like my Alt. is bad right? but I've got some old wiring so could that be why the Alt. is not recharging the battery or do the readings not account for wiring, basically what I'm asking is, do the low (almost non-existant) readings ONLY mean the Alt. is bad, or could they possibly mean that the wiring is bad so the Alt. is not getting enough power to charge the Battery, or the opposite, the power can't get from the Alt. to the battery, because the wires won't carry the current. But I'm pretty sure that if the Alt. was good, it would still read good if the wires couldn't carry the power to the battery, right? So like I said, sorry for intruding, but you sound like you know what you're talking about in this situation so I had to ask. So thank you in advance for any helpful information and/or suggestions.

With the key in position 2:
do see the battery light come on?
What voltage do measure at the small red wire on the back of the alternator?

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Yes, all my warning lights come on in key position 2, that's one of my problems, when I do get my car started, the damn warning lights won't turn off like they should. Anyway, the reading for the small red wire is 2.30 to 2.31.

I would then measure the voltage on both sides of fuse 13 and the small red wire alternator post while running.

The alternator will not start charging unless it has +12v on the small red wire.

BTW DO load test the battery and make sure it's not that. Batteries only last abt 2-3 yrs now, any more is bonus. check your terminals and make sure they're clean, on the battery and the car-any white sulphates-wash with warm water and baking soda solution-wipe dry with paper towel and discard. Guessing is not good enough-actually test it, even by charging and disconnecting it for 24hrs to see if it goes down. Hydrometers are usefull, sudden cold snaps are fatal for most old batteries. Using a DC AMP meter in series with your battery and absolutely nothing turned on, your battery drain must be much less than 0.25 AMPs average/minute. measure it and report. Caution: measuring current is potentially risky, especiailly if current is much more than expected. tapping the earth terminal on the battery will cause a large flash as things power up, and is not a good guide to the quiescent current. Start you ampmeter on the highest current reading and gradually switch to lower ranges in sequence until you get an intelligent reading. reverse connections if reading is wrong way. do not open the door or switch anything on whilst meter is in circuit. use the meter between the negative terminal and the earth wire only. Since you're measuring discharge, connect red lead to battery post and black lead to earth wirefor correct polarity!!!!!! Keep fingers away from connections, as excess current does make things very hot, should it occur. shorting the meter connected this way will not cause major troubles. If door lock solenoids are left on, I'd expect considerable heat from them, or anything else capable of draining a battery in 6-8hrs. On a 60AH battery you have to have a load over 5 AMP to do that, that's a minimum of 60W!!!! Something is getting hot!!! #2: there's a neat little solid state battery tester which can be bought from auto stores. It has several LEDS, and measures precise voltages to see if your alternator is working well enough, the 100%, 75% and 50% charge in the battery, and the cranking voltage (~8V). Ours is made by Arlec, and I've removed the battery clips and fitted a cigarette socket plug. Seems to work great after all these years, and is usefull to helpother motorists with quick diagnoses. Usually abt $15? Nothing to wear out or break, unless the car is wired reverse. Very handy. drop proof.

Battery tested fine, in good condition, which is what I'd thought because it's less than a year old and there hasn't been any cold weather lately, actually quite the opposite, very hot for this time of year, mid 80's to low 90's. Also, I don't have electronic locks or windows, so it's obviously not that, so I'm pretty sure it's the alternator, I'm taking it to be professionally tested tomorrow, I tested it myself, and it's dead, but before I buy a new one I just wanna make sure the old one is completely hopeless. But if you have anymore useful tips, suggestions or info. please feel free to keep it coming, and thank you all for your help so far, let's hope we get this right eventually.

if alternator shot, consider buying a used one from a wrecker and DIY fit new brushes, and bearings, and have the slip rings cleaned up via a lathe, & you will have a working unit good for years for a nominal sum. The most expensive usual failure is a regulator/diode pack. All else is pretty cheap: brushes $10- pr, bearings $20 or less, machining $20 or so-you do the rest. It's not hard, and provided you start with a working unit, a DIY recon is cheap maintenance. You will need some special tools, like a large pipe wrench, abt 3 -4" , a soldering iron, & a paperclip, and you may find it easier to cut (hacksaw) & replace the screws holding it together than try to undo them. I'll supply more detail if you want it. NB alternators generally, and the rest of the car, do NOT like being operated with the battery out of the car, or poorly connected-externally or internally. They then tend to wildly over-voltage-which can be terminal for the EMU , the alternator itself and every other electronic device fitted. I kid you not.