Author Topic: D- Alternator Connection  (Read 307 times)

Pawel66

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D- Alternator Connection
« on: April 02, 2024, 08:11:23 »
Even though worked over a couple of years ago, my alternator decided to stop working last night. Two questions, if I may:
1. Is the D- suppose to have ground (before regulator) at all times? From the wiring diagram it is hooked to directly to ground.
2. Where is this ground connection physically? Did not have much time last night, but it seemed to me it is somewhere on or near the oil pan starter connections plate. Is it there really?

I know my way around with replacement and overhaul, but I started to check things around. The first was to check if D- had ground. And it did not... I think it is supposed to...

Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
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lpeterssen

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Re: D- Alternator Connection
« Reply #1 on: April 02, 2024, 11:32:36 »
Dear Pawel

Yes “D-“ post is supposed to be grounded through the alternator body to chassis.  To check this out use a multimeter and check continuity’s between “D-“ post and the external shell of the generator.  Once this check passes, repeat procedure between that same post and your car body to verify that ground is passing through all components in the engine.

See diagram section attached.

If your alternator shell grounding is not good enough add simply a ground strap between it to the car body.

The original ground connection is at the engine side where the transmission bell housing has a large strap to body.

In my opinion there is no grounding post near the external voltage regulator.  I have not seen any derivation on the different wiring harnesses that I have refurbished so far, or maybe the shell of the voltage regulator makes ground directly to chassis through the mounting screws.

Best regards
Leonardo Peterssen
Www.wiredoktor.com

Pawel66

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Re: D- Alternator Connection
« Reply #2 on: April 02, 2024, 13:08:23 »
Leonardo, thank you for your kind attention!

I did a brief check when I got charging lamp permanently on, increasing intensity slightly as I revved up engine, going dark when I let it go down to idle, then getting bright at idle again.

Steady voltage 12.46V on battery regardless of revs. Headlights not brightening up on reviving up.

V-belt tight.

Swapped another regulator - same status. I concluded that alternator is shot, but wanted to check surroundings.

Saw on wiring diagram D- is fixed to ground. I checked the pin on the regulator plug vs. Car body - no ground. I took a piece of wire, connected the plug to ground - same effect, did not help.

That is when I had to leave it.
I do have additional ground strap for alternator.

The nearest ground point is the one for washer motor. But I think it is only for the washer motor.

I will do the checks as you described when I am back on Friday. Thanks again!
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

lpeterssen

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Re: D- Alternator Connection
« Reply #3 on: April 02, 2024, 13:17:49 »
Yes that is right, that grounding point near the wiper motor is only servicing that accessory , no one else

Always a pleasure to help people out with electric gremlins.


And yes, your alternator should be shot, since 12.46 volts is too low.  Minimum voltage for a healthy battery 12.6 volts.  Alternator in good working order should be above 13.9 volts.

Best regards
L.Peterssen
Www.wiredoktor.com

Pawel66

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Re: D- Alternator Connection
« Reply #4 on: April 02, 2024, 13:47:55 »
The 12.46V was after several kilometers drive with headlights on and without alternator...

I thought perhaps alternator is not working because something around it is not right - like this D- topic, that is why I asked to check. It seemed to me, but I had no time to verify that I saw the brown wire, that is coming out at D- location in the regulator plug, coming out of the harness down there near the oil pan connector plate. Need to verify that...

If the regulator housing was supposed to make ground through its attachment to inner fender, I think it would be marked on diagram as in case of the starter and attachment screws would be welded in, not just coming through the wheelhouse.

Thanks again!
« Last Edit: April 02, 2024, 13:54:09 by Pawel66 »
Pawel

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WRe

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Re: D- Alternator Connection
« Reply #5 on: April 03, 2024, 08:56:30 »
Hi Pawel,
have you read and tested like here described: https://www.sl113.org/wiki/Electrical/Alternator ?

Voltage and current are two opponents, which means that the more current flows, the smaller the voltage, and contact resistances have a greater effect at higher currents. Speed ​​also plays a role when it comes to power output. So if the battery is full and good, then the alternator with too little voltage may be correct.
It is possible that the voltage regulator is defective. The cable from connection D+ of the alternator could also be defective (cable break) or corroded at the connection. The plus and minus lines from the generator can also have a high resistance. The connections are often corroded.
...WRe


Pawel66

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Re: D- Alternator Connection
« Reply #6 on: April 03, 2024, 10:36:46 »
Yes, thank you. I know the piece from our Manual.

And exactly - I need to check the "surroundings", which is all the connections, I started with D- and it became suspect immediately. I will follow up on it when I am back home on Friday.

I swapped the regulator for a new one (NEW = Never Ever Worked). No change.

So yes - all the checks you advised are in front of me.

Last Friday I experienced exactly what you are saying in my W463 300GE. ABS not working, DRL working poorly, central lock not engaging from time to time - all that was about one corroded connection of + wire from the alternator. Once I cleaned it - all works fine.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
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Pawel66

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Re: D- Alternator Connection
« Reply #7 on: April 05, 2024, 20:30:58 »
Alternator was shot. I replaced it today with a refurbished unit bought on German e-bay (remarkable speed of delivery!) and all is fine. I will give my old unit to local Bosch service I have next door - we will see what they can do with it.

Bench tested all regulators I have - they are fine. The test in our Technical Manual is very useful.

Thanks Leonardo, thanks WRe for your kind attention.
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class