Well, you were right on the money with this one.

I got no movement whatsoever on the meter on a 10K scale. Full scale is 500K and the resistance was greater than the meter's capability to read it. If there's any leakage, it's smaller than this meter can measure.

To ensure that the meter functioned on this scale, I measured 30K through my body via my fingertips.

So, my original suggestion of 1000 ohms would definitely be too low..........a low limit of 10K would be much more realistic.

Ok, I've got baby sitting duty tonight, so I wasn't able to make it up to Autozone. I was able to test the alternator myself with my multimeter though. From the main terminals to the case the meter starts around 13M ohms then slowly builds if I hold the probes on it. After about 10-20 seconds, the resistance hits 35M ohms then my meter zeroes out with an M as the scale (I think this means infinity). If I test between the small terminal (the one that goes to the dash cluster) and the case I get a pretty steady reading of 69 ohms. So that would indicate that everything is ok, right? Is it normal for the resistance to slowly build like that?

Now...my starter that I had already diagnosed as junk...is checking out entirely differently in the house. Resistance between the large terminal and the case is 0 M (infinite I believe). Resistance between the small terminal and the case is 3-4 M ohms. I disconnected the wire between the solenoid and the starter motor before I brought it inside. This shouldn't make a difference when testing the big terminal should it? Incidentally, if I test the resistance between that large copper wire and the case it reads 0.1-0.4 Ohms. Even if that wire was hooked up to the solenoid, it shouldn't make a difference unless the solenoid was "energized", right? When testing the current while hooked up to the car battery, is it possible that I was partially energizing the solenoid through the meter? Just when I think I'm starting to figure this out too...

I wonder if I was touching the probes while holding them against the battery terminal and/or the wires. I don't think that I was because I'm really paranoid of getting shocked...but that might explain some of my gremlins. My body would carry a certain amount of amperage wouldn't it? Doh!!!! Ok, I'm second guessing everything now. If 2.6 Amps was flowing through my body, would I feel it?

did you check the ground wires to the engine and the battery terminals cleanliness etc?

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

The gradual rise you see is normal. It is known, when taken over a specified time, as the polarization index. The change you show is due to the insulation system "filling up" with charges, which polarizes the insulation and adds to its resistance. it is normal, and there is a minimum value (end reading at least twice the initial reading) that applies to older insulation systems. I would conclude your alternator's main winding resistance is fine, at room temperature. That is not necessarily the same story with the other windings. I am not sure this should be taken as a given for the other winding.

The same is true of the starter. There is a stator and a rotor, and each has a set of windings. Without a starter and alternator in front of me, or schematics I am not sure what terminals go where. And it is raining outside and cold, so I am not going to look under the hood.

The other issue is the windings get hot as the engine warms up, and then a variety of problems can occur. One is the standard weakening of the insulation system with temperatue, and another is geometry related - none of the materials in the device, including the insulation system components, have the same coefficient of thermal expansion. Thermal cycling is a design challenge for all machines, but very compact machines with high thermal cycling temperature ranges are especially challenged. The smaller the machine the fewer heat exchanging surfaces there are, generally, leading to higher temperature differences between the air and the metal. And worse, between parts of the machine with higher current loading and/or poorer air flow.

So, cold resistance readings are the first step. Put the thing in the oven and cook it to an even 250F or so and then take the readings again.

Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Yes. Because it would take (V=IR, with I=2.6 and R=30,000) more than 70,000 Volts to run that kind of current through you and the combination would be equivalent to over 250 horsepower and that would have killed you. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Ok, so at least my current readings weren't altered (significantly anyway) if I was touching the probes.

I'm hoping to pay autozone a visit tomorrow to test both devices, and then I'll post again from there.

Thanks again, everyone!

Yes, battery terminals were thoroughly cleaned and I get basically no resistance between the negative battery terminal and anywhere on the motor.

The saga continues...

So, both the alternator and the starter pass with flying colors according to the Autozone associate. I explained that I knew that both devices work but that I was having a problem with current drain. He then proceeded to check each device for resistance with his multimeter (same as you guys coached me to do). His results were the same as mine in the house, M ohm resistance or infinite, between the terminals and their cases.

Does anybody have any other suggestions? I'm thoroughly baffled at this point. How can both devices show a current drain when connected to the car, but infinite resistance on the bench? Bad engine ground? Shorted wire elsewhere?

check for any small coolant leaks in the area. I recall one thread where the member went through all sorts of hoops trying to figure out the electrical drain and it turned out to be a small coolant leak onto one of the electrical devices.
Probably only when car was operational.

does your trunk light work?
sometimes that wire gets chafed inside the bundle and is open. It may be a cause.
Also is your antenna motor functional? It may be stuck ON indefinitely.
Get into the trunk and unplug it then retest system.

__________________
1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Exactly - if you tested it with the wire disconnected between the solenoid and the motor and saw anything less than infinite resistance, that would mean there was a short between the solenoid contactors and ground.

Now, if you tested it with the wire connected, and see anything less than infinite resistance, it means your solenoid contacts are still touching, even when the solenoid is not energized.

If the wire is still disconnected, measure between the big terminal and the wire (with the solenoid de-energized). If there is anything less than infinite (0 Mega ohms) then the solenoid contacts are gummed up.

__________________
1984 300TD

I will check for coolant leaks, but I haven't noticed any.

My trunk lights all work, and so does my antenna (prior to removing the fuses). At the point of testing, all fuses were removed and the ignition switch, headlight switch, and transmission lockout/safety switch were all disconnected.

I was measuring 0.64A between the main starter wire by itself and pos. battery terminal with ground still attached to battery. Likewise, I was measuring 1.33A between the pos. battery terminal and the main alternator pair with the neg. battery still connected to ground. I really though that I had these components entirely isolated...until I removed them from the car and got contradictory results.

I think that tonight I'm going remove the battery from the car and use jumper cables to hook directly between the neg. battery terminal and the case of each device. I'll them measure Amperage between the positive terminal and the device. This should definitively tell me if I've got a current loss through each device...I think. Can someone please confirm whether or not this is a good plan?

The data is conflicting.

If the devices pass current when installed on the vehicle, and the amperage readings are correct as stated in previous posts, there cannot be infinite resistance to ground in the device.

The current must pass from the + supply to the frame of the vehicle to allow a reading on the ammeter.

So, either the original amps data is flawed or the resistance readings from Autozone are flawed. My bet is on the former. My opinion is further supported by the highly unlikely scenerio of three devices suffering from the same malady.

As I mentioned in other posts, digital meters typically allow for significant error by the operator and I don't condone their use by anyone who is not thoroughly skilled in their proper operation.

I haven't yet done that. I will check this tonight. Thanks.

I'm starting to come to that conclusion myself. I'm going to remeasure everything tonight. The only other variable that I haven't considered is the wiring, but the chances of both my starter wiring and my alternator wiring being chaffed to the point of grounding is pretty slim. I think my amperage readings must be inaccurate.

Is it a bad idea to "bench test" both devices by hooking the neg. battery terminal directly to their cases with a jumper cable and them reading amperage between the pos. battery and the main terminals of each device? I don't want to fry anything, but it seems like that's the way it's hooked in the car. I should be ok, right?