So I'm out of ideas guys...

I've posted about this situation before and I thought I had it fixed. 1992 300D 2.5, with charging issues.

Car has a new battery in it, tests good.

Alternator tested good, put a new voltage regulator in it just because, still tests good. Took the alternator to an automotive electric shop to have it tested NOT autozone, these are the guys who built my 190SL generator, etc. If they say it tests good, I like to think I believe them.

Cleaned the chassis to transmission ground.

Replaced the belt and tensioner, and now the car has a belly pan on it so water shouldn't make the belt slip (raining pretty hard tonight)

Replaced the alternator wiring harness (old one we discovered melted at some point in time and was poorly repaired)

Cleaned the battery to chassis ground.

My girlfriend drove the car for two weeks, no charging issues.

My dad came up from Cincinnati tonight to take the car home, 2 hours later the radio died, turn signals died, and the lights dimmed. Pulled in the driveway, shut it off, tried to restart... DEAD.

I noticed none of my girlfriends trips were over say a half hour. I've had alternators test bad when they got warmed up, but 3-5 tests on Autozone's testers generally got them warm enough to make them test bad. I would think the alternator would be up to a stable temperature long before the 30 minute mark, and way before the 2 hour mark. But could it be overheating and then functioning when it cools back down? Is there a way to test that theory?

I'm hitting my head against the wall here guys. Had the car painted, got the 1432 stereo working perfect, put an evaporator in it, did a 95 front end conversion, this is a hell of a nice car... that no-one can drive apparently.

Thoughts? Ideas? Anything is appreciated.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Does it have a "charging problem" bulb on the dash, like a battery symbol? If so, does the lamp come on when you turn to "run" before the engine starts? If not, that could be the problem if like my 1985 300D (all Motorola style alternators, including older GM). Mine needs current from the bulb to "boot up" the alternator's field windings. My Operator's Manual even warns to go immediately to the dealer if the lamp doesn't light. But a smart guy can change the bulb himself. An LED bulb will not flow enough current to bootup, at least not until you hit high rpm's. Many posts on this (including mine).

I had a charging problem on mine that was caused by corrosion where the regulator grounded to the alternator housing. A little cleaning and a dab of conductive grease and have had no issues for 5+ years.

However, do you have a multimeter? The easiest way to narrow down the problem is to check, across the battery, in both DC and AC with the engine running. You should have a charging voltage of ~13VDC and < 100mVAC.

If the DC is too low, then look at regulation (regulator, corrosion, etc.).

If the AC is too high, then rectification is the problem (diodes). (This will usually show up as abnormally high DC as well.)

In regards to the heat issue, it isn't uncommon for a/the diodes to break down after heating up, before failing completely.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Double check the entire path from the D+ terminal to the charging bulb in the cluster.

The bulb sits between switched battery in the cluster and the alternator D+ terminal.

If the bulb is open circuit or an LED the regulator cannot excite the field windings. No excitation = no electricity.

Yes you might manage to self excite at high RPMs but that is not going to give you sufficient charge. The residual magnetism will only produce voltage but no current to back it up.

As others said do a voltage check at the battery while running the engine at about 1.5 - 2k/min. You should get >13 V dc and < 100 mV ac.

If you have high ac content one or more of the 6 diodes (there are 6 because you have a 3-phase winding) has failed.

If your car has the 3-pole terminal block with 2 fat wires and 1 skinny wire, the fat wires are the B+ to the battery (alternator output) and the skinny wire is the D+ (regulator control via the charge light). You should have battery voltage at the D+ when the key is on but the engine is not running. Once the engine is running the voltage will remain. This is how the regulator regulates, it is the feedback from the system voltage.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I beat my head working on my 85. Turned out to be worn out insulation on the alternator wiring harness AND a bad neutral safety switch. You already fixed the wiring harness, and a bad NSS doesn't make the lights dim. Have you done a battery drain test?

__________________
2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900

Maybe a long shot, but are you certain the glow plug relay is releasing? Several years ago I chased a similar sounding issue for weeks before finally discovering that my glow relay was remaining closed and drawing more current than the alternator could keep up with. To make it even more fun to troubleshoot, it wouldn't do this every time I started the car. I eventually figured it out and replaced the relay. Problem solved.

__________________
Joe

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1980 300SD - 495k miles - 'The Ambassador'
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Former Family Members
95 C280
73 280SEL
90 300D
87 300SDL (X2)
86 560SEL
84 300D
80 300SD

Simple things first =>

Have you measured the generated voltage? (You don't actually mention that)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I'm posting from my phone so sorry for the lack of detail, or grammar.

I drove the 190D down to Cincinnati yesterday afternoon. My dad had put the 300D battery on the charger all day. Car fired right up and I drove home to Columbus. Ran the heat and the stereo the whole way. Never lost electricity. Shut the car off at my warehouse, walked through opened up the gate, got a soda, etc. Let the car sit a half hour so it would cool down. Got in it, glowed it, fired right up. So it appears the battery charged on that trip.

To answer your question stretch, last week the car was idling at 13.7 volts.

I did the key on test. none of the dash lights self check. Only the glow light comes on. Set the parking brake or turn on the high beams and those lights will come on, so its not a cluster grounding issue. Pulled the cluster out and the battery light bulb appears good.

Stumbled accross this in my googling
W124 woes - self test lights [Archive] - Mercedes-Benz Owners' Forums

So I think my issue is with the D+

I will check it at the alternator, but the b+ goes from the alt to a junction block and then from the junction block to...?

If I remember correctly the 92 has two blue D+ wires leaving the junction block. Can a anyone tell me where they go after the junction?

Also does anyone know what bulb is in the battery light. I called the dealer and its sort of ambiguous in the catalogue.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Sylvania 2721 I believe are the indicator cluster bulbs.

That 13.7 is just at idle? With what turned on?

Turn on the average load (light, blower, etc) and see what the voltage drops to.. rev up to 1500 or 2000 and see what it is with that same load.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I'll nit-pick at your post, not to be a prick, but to hopefully identify your problem.
Hardly convincing. Your car has a big battery. Might go a week after being fully charged.
Sounds about right. Most cars show 12.6 V with the engine off and 14.3 V with the engine running (working alternator). I use a cigarette lighter voltmeter in all my cars. Check Amazon and ebay. Harbor Freight sells one w/ LED lights for ~$4 on sale.
Read your Owner's Manual. Mine says to drive immediately to the dealer if the battery warning lamp doesn't light after you power the dash, before starting the engine. In my 1984 & 1985 300D, the "low fuel" and "caliper pad worn" bulbs also light. I don't know if that is for a "bulb check" or as backup "boot-up" current for the alternator field. Maybe both.

Just looking at a bulb is not a valid test. My dad did that with a glass fuse and we suffered 5 yrs with no car AC in Florida when I was a kid (fuse was melted at end). With the bulb in the holder, use a multimeter to measure ohms between the two terminals. Infinity is bad, good is <100 ohm.
I recall the "boot-up circuit" is called "D+" in my cars (all Motorola-type alternators). The wire runs to a single-wire round connector that is strapped to the aft side of the coolant reservoir. It looks like the round temp sensor connectors.
In my cars, the alternator output is on two "B+" spade terminals that run in parallel to the same place - the junction block in front of the battery. Why 2 wires? My guess is that other cars that use the Bosch alternator run the output 2 different places. M-B didn't.
I recall the bulb# is listed in the Owner's Manual. Same bulb as all the other ones in the big holder. Any 12V bulb with the correct terminals will work if it fits. I bought LED bulbs on ebay, then found the LED doesn't work for that BATT lamp (not enough current), but they work fine for the others (dash lighting). BTW, if using LED's, insure they don't short circuit the bulb holder as many do (read posts).

You are correct, I was talking about the D+ but incorrectly wrote B+, I changed by post, thanks for catching that, that should clarify for others.

I do not have the owners manual to this car.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

Nothing about this car is convincing, I was merely remarking as to the cars performance yesterday. I started the car 4 times yesterday and it started strong every time.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

A diesel has no electrical ignition system, you can run the radio for a month on a fully charged battery. You've been told the correct answer. Replace the bulb in the dash and the alternator should start working again. The circuit is simple: one side of the bulb connects to switched 12v+ through the ignition switch, the other end goes to D+ on the alternator. It sounds ridiculous, but the bulb grounds through the VR, and by this means supplies bootstrap voltage for the alternator. If you want to prevent this problem in the future, you can solder a 330 ohm resistor in parallel with the bulb. If there's enough residual magnetism in the alternator core, it can produce enough current to bootstrap itself, but not reliably.

Having no bulb self test is a dead giveaway for a break in the D+ circuit. All the self-testing bulbs feed, via diodes and resistors, to the D+ line and eventually to ground.

The bulbs that should light up at startup, in addition to the charge light, are:
Low oil level
Low coolant
Low fuel
Low washer fluid
Brake pad wear
Park brake/low brake fluid

Every one of these bulbs is driven by a sensor that grounds the line from the bulb. Exception - low oil level, in that case open circuit from the sensor causes the bulb to turn on, there is an electronic circuit in the cluster to drive this.

The other side of these bulbs are connected to the switched battery line in the cluster.

Once the alternator begins to produce output, then the potential goes to zero across both ends of all these bulbs and they turn off.

Remove the D+ line from the alternator (the single skinny wire). With the key on but the engine not running momentarily ground the D+ line. See if the cluster bulbs illuminate.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

I just played this game. Did the alternator upgrade on my 87, used a 92 300E alternator. I swapped the wiring harness and terminal block to accommodate the larger cable from the alternator.

There should be 3 D+ wires at the terminal block.
One to the alternator D+ - white jacketed high temperature wire with blue stripe.
One to the cluster for the charge light and warning light self test (pin 9 on the big circular connector) - solid blue.
One to the ABS controller N30 pin 15. I suspect this is how the ABS controller knows the state of the electrical system of the car - blue with red stripe.

B+ has two terminals to accept the two output cables in parallel from the alternator - two white high temp with red stripe. The two B+ terminals are internally connected in the terminal block.
At the B+ block there is also a battery feed cable - red
also a feed to the main power block under the drivers side of the dash - red
also a feed to the aux fan and another to the OVP relay

I would go to w124-zone.com and get the diagram. Somehow their copy is cleaner than the one on the MB Startek site.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech