Hello, We put in a new voltage regulator today and the multimeter showed charging at 14.47. So I was thinking I had my problem fixed.

I was getting a reading of 17.81 from the last regulator. Was told it was way too high
...car was run less than 5 minutes like this and the battery is brand spankin new.

It was fully charged before installation.

After checking the battery with the multimeter(14.47) I got into the car and turned on the blower motor...then noticed that the battery light would come on faintly. I shut the blower motor off. I went back and checked the battery and now am getting 12.37 volts. Got in the car and reved it to 2000 rpm and it seemed that the battery light is fluctuating from bright to faint regardless of rpm or of the blower motor being turned on. The car is a 1988 420 sel I am trying to get out of the garage. It has not run for at least five years. Thanks

With the engine running, place a multi-meter across the battery terminals and check for AC volts. If it reads more than ~100mVAC, then the diodes in the rectifier are breaking down. Don't run it for very long as the high VAC may damage your new regulator, if it hasn't already. This is why I disagree with the advice, given by many, to change the regulator as the first step in troubleshooting the alternator.

Any time there is a problem with an alternator not giving the correct charge, it is very important to check both Volts AC as well as Volts DC. The alternator has two tasks, rectifying the AC to DC and regulating the resulting DC.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Did you check the brushes?

Is this regulator the rectangular bosch type that bolts onto the alternator with the brushes built in?

If it has built in brushes, was there a brush hold back pin? Did you pull it out after installing the brush / regulator package?

You have a bad lead/connection on the main lead from the alt to the starter/battery. I had this problem & ended up installing a new wire from the alt to the battery.
It could be a dirty connection or a break in the thick wire.
If you run the car with this situation for a while, you will fry your new reg. Never run the motor without a battery.

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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 think this may be my current problem.

I replaced the alternator after replacing the VR because I was only getting 12.37 volts. Took the alternator to a store and got a new one because testing also showed the alternator to be bad.

No one has been able to coax more than 12.38 v out of the new alternator. I have been driving the car during the day when that's the only time it could be used.

Today on the way home I had the blower on for a minute and the battery later showed the idiot light for lack of charging.

I will investigate this Saturday or during the weekend.
Thanks for the tip

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Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

Don't forget ot clean the contact areas of the Chassis to Engine Ground Starp and of couse the Batter to Chassis Ground Wire.

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84 300D, 82 Volvo 244Gl Diesel

I have cleaned all contacts mentioned. I have even added a new ground wire from the alternator bracket to the fender close to the main ground off the battery. I now have 14.47 after starting the car down to 13.11 after 10 minutes of idleing.

The battery light is still intermitantly flickering. It seems to almost come all the way on if I turn the blower motor on. If I turn the blower motor off... the battery light goes out, but then if I rev the car up the battery light starts to fade in. I have also noticed that my signal lights are not working.Tried the emergency flasher and they are working.

Where is the flasher relay for the signal lights?? I wonder if something electrical is stuck causing these problems with that battery light. My srs light is on and the abs light came on again after running for a few minutes. I played with the fancy power seats and started to go up with the headrest and then it stopped and would not go back down. The radio will not turn on. There are just dashes across the screen. I fixed a few burnt out taillights. I have electrical gremlins from sitting for so long.

I have access to a fairly complete parts car so I could start robbing relays, but which ones. I am new to this type of car.

Forgot to mention that there is a strange yellow light on in the instrument cluster that has an exclamation point. What is that all about.

Yes we installed a new voltage regulator so it has new brushes. the new regulator had a plastic cover on the brushes and they popped out when it was removed ...no pin to pull. It looks abit different than the bosch regulator. It actually looks alot like the regulator we took out that was overcharging.

I cleaned all the contacts on the alternator as well as the little junction block on the fender where the wires all collect with the little blue wire. Cleaned the short main ground and checked the continuity with the meter. cleaned the fender up where it mounts. I cleaned all the bolts up shiny with the wire wheel and used copper antiseize on the washers and connection points as well as the screws and bolts for all the main wiring lugs. I have pretty much eliminated all possibilities of it being a bad connection in my opinion. The only thing that it might be is a wire broken inside the insulation...which you mentioned earlier. I should be able to check continuity on those. Thanks

I still have to do this one. I forgot and now it is dark out. I will try this tomorrow and check continuity from alt wire to the junction block. Thanks

Maybe the Slip Ring on the Alternator is in bad shape.

What did the Sip Ring on the Alternator look of Feel like. (With the Voltage Regulator removed there is room to stick you Finger in; Engine not running of course.)

What were the results of the AC Voltage Test that was suggested in post #2?

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84 300D, 82 Volvo 244Gl Diesel

Hello, I have been enjoying driving this car. I checked the a/c volts at the battery with the car running. I got between 30.4 ac and 30.9 ac when reving the engine a bit. I get 14.4v dc. and the battery light still is faintly glowing, mostly with the blower motor on for the heat.

I am not sure if the blower motor or something on that circuit would cause this?

I have the srs light always on and the abs light comes on from time to time. I read that might be rectified by cleaning sensors and contacts?

I took the car on a highway trip and it was nice. It started everytime.

Since returning from the road trip, I have swapped in a used OVP relay and there was no change with the lights on the dash. I have another OVP relay but it has two fuses in it and two more pins at the plug side? It came off the same model/year car....so why the difference.

I had some brief performance issues on the road trip that seemed to improve after a bottle of injector cleaner. I think a fuel filter might help and have purchased a wix brand one of those.

I think the cap and rotor are original as the srews are rusty. That may solve the intermittant idle and performance issues? I am checking it tonight maybe.

I think this needs to have the timing checked. How to? Thank you

Attached Thumbnails

         

This is the black OVP relay that came out of the current running car. The red one in the pics above is the other spare out of the same model and year of car ....1988 420sel. why the difference? I think this black one still works cause the other black one that replaced it did not change any of the electrical issues on the dash lights. fuses are good.

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A good start would be to completely isolate the alternator from the car wiring, then make a direct connection from the B+ point to the battery positive, a wire from the D+ point to a 3W bulb with other end to positive, it should light up with a stopped alternator, start engine, light should go out and it should work correctly, If not - your alternator has internal problems mostly leading to bad slip rings.

If the above test corrects your situation, then a good place to start troubleshooting is to check that you dont have a higher wattage bulb in the instrument cluster for batt warning or the wire connections being dirty and that your main power cable to the alternator is not bad.

I faced a similar problem in a VW golf diesel once, and the problem was the thin blue wire from D+ (light) was pretty corroded on its connector beneath the battery. it used a similar Bosch 90A alternator.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)