W123 not charging, dummy lights off with key on - Page 5 - PeachParts Mercedes-Benz Forum

Diseasel300 · #61 01-26-2018, 11:26 AM

Quote:

Originally Posted by funola

The 6 bulbs (with the isolation diodes in series) has a 0.7 V drop across each bulb, the charge bulb has no diode in series thus no V drop. The brake warning to the right of the charge indicator is almost as bright as the charge indicator. Since the other 5 bulbs are in parallel with the brake bulb, they should all light up with the same intensity as the brake bulb.

Something else funny going on in there.

When there's a "fake" ground path, traditional logic and reason fly out the window. Whichever bulbs have the highest wattage filaments will glow first. The lower wattage bulbs will glow weakly if at all. You're dealing with current potential here, not voltage potential in the traditional sense.

Nothing in the cluster can cause this behavior from the typical flaky ground issues, this is an alternator problem - and a weird one at that.

arcticathlon · #62 01-26-2018, 04:20 PM

So i took off the voltage regulator and here is what i found.

i then took some 600grit sand paper and clean the surface. I kept bumping the engine to rotate the alternator and this worked really well.

I then checked and the the weird instrument light action is still happening. I then checked the voltage of the battery with car off and it was 11.74v. I then turned on the headlights and then started the engine. the video below is what i saw. The alternator was only increasing voltage to 12.8v. If i revved the engine then it would increase to 13.6v, but that was it. With engine off the voltage would drop below 11.7v.

https://youtu.be/wnW7gB3V2Lk

I think i need a new alternator.

Diseasel300 · #63 01-26-2018, 04:27 PM

I think it's worth having the battery tested as well. Most auto parts stores will do it for free. Even with the alternator only putting out 12.8V, I'd still expect battery voltage higher than you have. You could have a situation where the battery is failing and has damaged the rectifier pack in the alternator. Not a common situation, but I've seen it happen twice in my life so far.

funola · #64 01-26-2018, 04:36 PM

Did you measure alternator voltage for AC as suggested already? Set DVM on the most sensitive AC scale.

arcticathlon · #65 01-26-2018, 04:55 PM

Quote:

Originally Posted by Diseasel300

I think it's worth having the battery tested as well. Most auto parts stores will do it for free. Even with the alternator only putting out 12.8V, I'd still expect battery voltage higher than you have. You could have a situation where the battery is failing and has damaged the rectifier pack in the alternator. Not a common situation, but I've seen it happen twice in my life so far.

Well i also assume that the battery has not gotten a good charge from the Alternator. Since i have picked it up, it has not been driven more than 200 miles and so I would think that the battery is not fully charged. I will take it to have the battery tested.

If it is good, then i will swap out the alternator.

arcticathlon · #66 01-26-2018, 04:56 PM

Quote:

Originally Posted by funola

Did you measure alternator voltage for AC as suggested already? Set DVM on the most sensitive AC scale.

I can't test until tomorrow, as my wife and i are planning on painting rooms in the house, and i am now in the process of preparing for that.

funola · #67 01-26-2018, 05:13 PM

Charge the battery overnight before bringing it in for a test.

Diesel911 · #68 01-26-2018, 05:34 PM

aaaaaa

Diesel911 · #69 01-26-2018, 05:51 PM

Long time ago I got a used Alternator Connector from the Junk Yard and made an alternator test cord.
One person over on benzworld also made one.

The cord can save you the labor of pulling off you alternator to have it tested.

The Light Bulb in the circuit duplicates the Charging Light Bulb and supplies that bit if resistance needed for the alternator to charge.

If your alternator will not work with the test cord and it is not a problem with the alternator being grounded there is some issue inside of the alternator or the regulator.

Note that all of the wires connect into one wire that goes to the Positive Battery Terminal.

If the alternator works with the test cord but not when the normal connector is plugged in you have some issue from the normal connector back.

Also because the same alternator connector is used on lots of other cars with Bosch alternators from that same era you can buy new connectors or if Mercedes still has them the individual parts or the connector.

Mxfrank · #70 01-26-2018, 06:43 PM

You don’t need a test cord. There is a thee position connector on the right fender, just forward of the battery. Two of the connections are the B+ leads, the third is D+. You can unbolt the terminals and isolate the alternator, then test to your heart’s content.

optimusprime · #71 01-27-2018, 05:17 AM

Can i ask one question and then i will go away .
After you switch the ignition on first is the battery charge bulb lit up?

arcticathlon · #72 01-27-2018, 09:40 AM

Quote:

Originally Posted by optimusprime

Can i ask one question and then i will go away .
After you switch the ignition on first is the battery charge bulb lit up?

https://youtu.be/BYOlO_MZ-Mg

Here is a video of the start up sequence and after it is started. I also see some lights on the right side (bulb warning and washer fluid level) that also are lighting up. I did not notice them before, or was only focused on the left side.

Diseasel300 · #73 01-27-2018, 10:39 AM

The washer fluid level lamp is tied into the rest with the field flash circuit. Just further evidence to a bad alternator. The bulb warning indicator as far as I can tell, is not tied into that circuit, however it can have flaky behavior when weird grounding issues develop.