-just had front end suspension and total steering redo done, gear box and all...got the car back and would not start next morning...took it to AutoZone and was told alternator is bad...don't believe in coincidence...checked connections to alternator, leads, etc...pulled instrument cluster and bulb is good although it does not light up when ignition is turned on...don't remember if it ever has...any ideas???

1983 300SD

Best guess:
Voltage regulator failed.

The 300SD requires the Long Brush unit..

Voltage Regulator, Internal Type (Long Brush)
MB# 002 154 72 06

Check AllPartsExpress in the Buy Parts tab.

I had the same problem last week. Advance Auto told me I needed a alternator also. I took it home and replaced the volt reg. thinking that would do it. It didn't so I ordered an alternator. Long story short: alt. was fine, had a bad wire between the alt. and the battery. Where it passed through a grommet it had broken and only two strands were still connected. Replaced the wire and all is well.

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Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K

if the bulb is good with the key on and engine off check for battery voltage on the small alternator wire at the alternator end of the wire with it disconnected from the alternator.No voltage will mean a problem in that circuit,try to follow that wire back and check wherever you can for corrosion or a break in the wire ,will be a big help if you can locate a wiring diagram for your year/model.If you have battery voltage on the wire and touch that wire to the case of the alt while someone watches for the light on the dash,it should light,if it does check for battery volts at the large wire,if you have correct voltage on the large wire chances are you have another bad alternator.When you resolve the problem please come back with the solution so that we all may learn from your experience. Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles

As a result of pulling the instrument cluster to check my battery light, I replaced the gears for the odometer. It has gotten dark here in the Raleigh, NC area after installing the repaired cluster, I noticed the faint glow of the battery light with engine running. I am intalling a new Bosch alternator this weekend and hope this is the problem. Is there a reason the bulb is glowing so faintly? Should I replace the bulb?

There is a slight voltage potential between the two leads going to the bulb. One lead goes to the alternator and probably sees 13.5V............the second lead goes to the battery and sees 12V. The difference will allow the light to barely glow..........you can only see it at night.

The SD would do this at times, as well.

My experience with a faint battery light is a failed diode within the alternator.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Yep, I've heard that is possible, as well. I have to check that out on the SD.

I had this problem. Ended up that the main wires from the alt to the battery were not making proper connection. I put a new wire direct from the back of the alt, attached to one of the thick wires on the plug,direct to the battery. The problem has not come back.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

It could be the situation that a marginal cable results in the voltage differential at the bulb. With a proper cable, the voltage is the same throughout the system. This makes more sense.

I recently restored the cable to the back of the alternator on the SD.............one of the two had broken off the terminal end...........so, now I need to check if that light still has the glow at night.

Brian,
I only worked out the problem because when I checked the voltage at the back of the alt, I had 13.5 & 12 at the battery at the time. if I put the lights & other stuff on it got worse. Couldnt work it out as there was meant to be a couple of thick wires between the 2. The new wire fixed the voltage difference. I have no idea what is wrong in the loom with the original wires, will leave that for another time.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I had the two thick wires as well. However, one of them was hanging by a thread and all the work was done via the second wire............clearly insufficient.

I've got to check the SD tomorrow and see if that ghosting is gone. Maybe it's not a normal condition on these vehicle after all.

I had that "ghosting" once due to a bad alternator (diode, I guess), but I've also had a bad connector on the back of the alternator cause reduced charging. There are two wires that run in parallel, in my case they were both nearly corroded off the connector. After repairing the connector, all was good.