I have an '87 SDL and am having a problem. The battery/alternator light stays on after the car is started. It never goes out. The light gets brighter as the rpm's increase and dimmer when they decrease. After doing a search on the board I have tried the following:

1. Measured voltage at the battery. It's right at 14V with no accessories on.

2. Cleaned the battery terminals.

3. Replaced the voltage regulator.

The car seems to run fine. No problems with any accessories (headlights, AC, etc.). Is the next step to replace the alternator?

Thanks for your help,
Brian

When you checked the voltage does it fluxuate dramtaically when going from idle to partial throttle?

14 V is good charging so I would tend to think it is not the alternator but maybe it is sensing other problems in the charging system i.e. voltage regulator.

This is too new of a model for me... but maybe someone else cna help out...

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Well, when I went out this morning I checked the voltage after starting it up and it was at 16V. I hopped in and took off and the light was on brighter than ever. Dim at idle but full brightness around 1500rpm. A little later in my drive I got on the pedal and when it reached about 4500 rpm the light went out. It still hasn't returned yet. I will take some more voltage measurments this evening to see if maybe it has calmed down.

Sounds like you may be losing your voltage regulator. 16V is high on a 12V system. I think mine on my old Dodge MH maxs at 15.1 volts which I have been told is borderline.

You can take it by an auto parts place and most of them will check these for free looking for the sale.

An '87 is way out of my range of experience to be able to help much. Sorry.

I think a lot of the older alternators on these cars and maybe yours have an external voltage regulator and they are pretty simple to replace.

Maybe try a search on this topic at the bottom of the page. Or to see if your model and year have an external regulator you can always go tot he fastlane link at the top of this page, go to their online catalog and see if this part is listed.

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

The voltage regulator is very easy to replace.

I just replaced my entire alternator (about a week ago) because the brushes had worn out. I could have just replaced the brushes, but I didn't. Why? I don't know.

Anyway... when my alternator died, I just had a flickering battery light at idle... no light at all above 1000 rpms. When I tested the voltage at the battery, it was 13V at idle, and 12V at 3000 rpms. After driving around with the headlights on for a while, the voltage would drop to 10V, and the ANTILOCK light would come on (as it is supposed to).

It doesn't sound to me like you're having a problem with lack of charge... it's possible that your regulator is heading south for the winter.

Keep taking voltage measurements and let us know if the light comes back on... very odd.

Do NOT drive the car.
Replace the regulator or alternator as needed to fix the problem.
A few weeks ago; had a ricer in the shop, output 18.5V, and electrical system was toast.
Right around 16V is where bulbs start popping like fuses.

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While driving home this evening I noticed that at some stop lights while idling the ABS light would come on until I started moving again. Still no battery light. I tested the voltage again when I got home and it is now hovering at 12.5V while running and about the same when the car is off. The readings don't seem to be very consistent. So far I've got:
8:00AM engine cold: running(16V) battery light on.

5:30PM engine hot: running(12.5V) no battery light but intermittent ABS light.

All accessories continue to work as normal. I'll get more readings tomorrow morning. I'm going to pull the voltage regulator and make sure I've got it installed correctly. If I installed it properly then I'll go ahead and try replacing the alternator and see what happens. I appreciate all the help/advice and if there is anything else I should look for please let me know.

Brian

The ground cable from engine to body, if broken or heavy corrosion, replace it, any auto parts store will have generic ground straps.

Too high, possibly blew the diodes or regiulator

Quote:

5:30PM engine hot: running(12.5V) no battery light but intermittent ABS light. All accessories continue to work as normal. I'll get more readings tomorrow morning. I'm going to pull the voltage regulator and make sure I've got it installed correctly. If I installed it properly then I'll go ahead and try replacing the alternator and see what happens. I appreciate all the help/advice and if there is anything else I should look for please let me know. Brian

go to the wreckers and buy an alternator for your car, or to the Auto Electrician and have yours rebuilt.
You are no-longer charging the battery and will end up stranded if you don't fix or replace the alternator very soon.

__________________
Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.