Alt light came on, so did the reserve and brake wear lamps - PeachParts Mercedes-Benz Forum

Crackstar · #1 07-09-2010, 10:11 AM

1983 300TD Wagon

What does this mean? Are all three bulbs supposed to come on when the Alt fails? Its really odd seeing as I don't have the Brake wear probes hooked up. The battery tested bad as did the alt, so both were replaced, I had the alt checked before I installed it and was told it was good. Now none of the lights come on any more, I pulled them out and tested them and they all still work. Yet I still get no sort of charging action on the battery. car off 12.5v car running 12.5v, rev it up 12.5v

What the hell is so screwed up all threee lights came on?

Why won't my Reserve light come back on now?(When I'm out of fuel)

Is this a sign of a fubar'd Instrument Cluster?

Can the charging system be bypassed out side of the I.C.?

I assure you I have been searching and reading everything I can about tthis charging system. NOthing seems to match my problems. I have checked every connection for cleanliness and tightness. all clean all tight.
I've checked as much as I can figure out of the wiring from the alt and every thing I can find seems ok (continuity)

I really thought it would be as "simple" as replacing the alternator, but I was wrong, how did I break my car?

thanks
chuck

vstech · #2 07-09-2010, 02:37 PM

multiple electrical problems can usually be traced to ground issues.

Crackstar · #3 07-09-2010, 03:00 PM

Could some one help me with some specifics?

Do I need to pull my Instrument Cluster out to look for debris, shorting something out? Is that even likely?

Is the three lights on a "total failure" of something else?

How are the Reserve light and the brake wear indicators even linked to the Alternator light?

I wonder if I put the old bad alternator back in if all three lights would come on again?

If anybody wants to help or has any ideas I'd love it

79Mercy · #4 07-09-2010, 03:03 PM

Sometimes when the voltage regulator is bad none of the dash lights will come on. Swap your voltage regulator from the old alternator to the newer one if it is still good.

Crackstar · #5 07-09-2010, 03:17 PM

How quick do you think a VR in a remaned alternator can go south?
How can I test the pile of voltage regulators I have? Seriously I have like 6 from other swaps and VR failures in the past.

But I had the new alt tested before I installed it? Could it have fried at Advance on their machine?

Also, before I did the alt swap I put in a new voltage reg to see if the cheap route would fix the problem. The lights went out for one ride and came back on the minute i slowed down to get off the interstate.

79Mercy · #6 07-09-2010, 03:19 PM

Im not sure, its hard to say on the internet. But im willing to bet the voltage regulator is bad. Pull it out and take a look at the brushes and the connections.

atomix8 · #7 07-09-2010, 03:44 PM

If those lights were on, and are still on on the cluster, the car doesn't think it's turned on yet. I believe I read this was a voltage signal...mine lit up when I threw an alternator belt a month or so ago (brake pad light & charging at least...maybe the "BRAKE" light too, certainly most of the warning lights.)

That just gets you back to a 'no charging' case, which you knew. If you want to build a test cable and load (who does?) the red wires coming out of the back of the alternator carry the charging current. I suppose you could get a voltage drop reading off them with just a multimeter, but that's not the right charging load by any means.

snookwhaler · #8 07-09-2010, 04:08 PM

Quote:

Originally Posted by Crackstar

1983 300TD Wagon

What does this mean? Are all three bulbs supposed to come on when the Alt fails? Its really odd seeing as I don't have the Brake wear probes hooked up. The battery tested bad as did the alt, so both were replaced, I had the alt checked before I installed it and was told it was good. Now none of the lights come on any more, I pulled them out and tested them and they all still work. Yet I still get no sort of charging action on the battery. car off 12.5v car running 12.5v, rev it up 12.5v

What the hell is so screwed up all threee lights came on?

Why won't my Reserve light come back on now?(When I'm out of fuel)

Is this a sign of a fubar'd Instrument Cluster?

Can the charging system be bypassed out side of the I.C.?

I assure you I have been searching and reading everything I can about tthis charging system. NOthing seems to match my problems. I have checked every connection for cleanliness and tightness. all clean all tight.
I've checked as much as I can figure out of the wiring from the alt and every thing I can find seems ok (continuity)

I really thought it would be as "simple" as replacing the alternator, but I was wrong, how did I break my car?

thanks
chuck

I went through something very similar earlier in the year. My problem turned out to be a bad regulator. If you have a meter, you can check a few things to identify a bad regulator (in the car) very quickly.

Here is that thread:

http://www.peachparts.com/shopforum/showthread.php?t=271992&highlight=voltage+regulator

hey_allen · #9 07-09-2010, 07:17 PM

I'm not sure that the wiring is the same, but when my SD had those lights come on, as well as the batt light getting brighter with RPM increase, I finally tracked it down to a failed diode in the alternator's rectikfier.

It was also easily visible once I hooked up my oscilloscope, having a deep drop in the pattern every sixth wave.

If youb have the ability, try another alternator, or make sure you have continuity on the wire that goew to the gaudes from the alternator.

Yak · #10 07-09-2010, 09:57 PM

You may have two problems.

Some questions to clarify: Were you having charging issues BEFORE the lights came on? Or did the lights come on, so you assumed charging issues and then had the battery and alt checked?

Is your battery currently discharging and not being recharged at all? It sounds like you're measuring a steady 12.5 V at the battery, so you're maybe treading water as far as charging?

The bulbs ARE all connected on the same circuits in the cluster. And then they're linked to the alternator.

I had the same lights come on after I did a cluster rebuild. I removed the cluster, double-checked all traces and connections, added a little contact enhancer and then put it back in and the problem went away. You might have a short across a trace on the cluster causing the lights to come on. If you have the wiring diagrams in the FSM (do a search for "wiring diagram" and you'll find the links) the bulbs are b, c, d, and i in the cluster. So you could have a cluster problem with the lights.

But the problem might also be caused by a bad alternator (or diode, or regulator) or alternator connection. Have you checked out the diesel giant pictorial?

http://www.dieselgiant.com/mercedesvoltageregulatorinstall.htm

Those pics are from the bottom looking up. Do you see the small push-on connector with the snap-clip? In the pics, he doesn't have his clip connected correctly.

From above in your car with the intake tube removed you can actually see the blue wire that connects directly back to your IC and your four lights. I'd start with the easy step of pulling this clip off, cleaning and inspecting it, then snapping it back on securely.