My battery keeps going dead. I replaced the battery. I pulled the alternator and took it into Canadian Tire and had it tested, and it checks out as good. I put in a new alternator about 1.5 years ago, a bosch premium re-built. The belt tension seems good in that the alternator pulley is difficult to turn by hand.

The alt. belt had been squealing. Usually I could get it to stop squealing by turning off all electrics, like the heater, radio, seat warmers.

Any ideas??

The car is a 1989 420 SEL with 245,000 KM

__________________
1989 420 SEL

Have you cleaned the inside surface if you battery terminals? If they have a corrsion built up then insufficient charge is reaching your battery causing it to periodicly go dead.

if not

It could be the voltage regulator built into the alternator. It can be replaced without changing the altinator and is a much cheaper fix.

also

You should increase the tension of your belt. (if required)

__________________
Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

Do you have an alarm system in your car?

__________________
1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

I have only the factory installed alarm system in the car. I have no owner installed accessories in the car. All original equipment.

The battery terminals are clean. They have no corrosion on the outside or on the inside. I used one of those circular battery wire brushes.

I do have a spare voltage regulator. But shouldn't the defective regulator show the alternator test?

Any thoughts? Could it be the wiring harness? I see the positive wiring harness retails for about C$320, part number 126 540 25 30, which I would prefer avoiding. Maybe the juice is not getting from the alternator to the battery? I guess I could test it - check voltage at battery before starting, then start, check voltage at battery and at the B+ terminal of alternator. If B+ and positive battery terminal read different voltages, then the cable between the two is bad, especially if the battery is lower voltage than the voltage at the alternator b+. Right?

__________________
1989 420 SEL

Put a DC voltmeter across the battery and see that it is putting out about 13.5 to 14.5 volts with engine running and reved up. Just because you replaced it, even if it was yesterday, you don't know if it's working right without checking it.

Hope this helps,

I agree,

Sounds like the voltage regulator. The brushes are probably worn out.

Just my 2 cents...

If Larry's advice checks out and you do happen to get the proper voltage output from the alternator, then it's time to see if you have a small electrical leak.

Disconnect the negative battery terminal and connect an ammeter that can read milliamps between the negative battery terminal and the cable clamp.

Watch the meter. You should get a reading below about 60 mA. If it is above 100 mA, you need to start pulling fuses to see which circuit is drawing the most power. Also, remove all the wires from the back of the alternator to determine if the alternator has a small leak.

When you find the culprit, the ammeter should get down below 60 mA, or about.

it also depends on the brand of the battery. DO NOT, i repeat DO NOT buy Everstart or Exide brand batteries for your Benz (any Mercedes). Any technician can tell you about past issues with these batteries. With Exide, after about two years, the battery starts to trap and collect all the sulfur on one side and ends up blowing up on its side due to heat and sulfur mixing together (slight heat from engine). With the Everstart, the battery simply sucks. It stresses on the label that it carries 875 ca, but that's only for about one month of use. What do u think the ca's will be in three months or one year? Definitly lower than half the original amount. That's where retailers like to get you by the neck and screw you over with the "warranty". So much for a 7 year warranty...

The only three brands that I can really depend on are Interstate, Duralast, and defintly DieHard (international).

I had one MB Tech tell me, around the first times I drove my 86' 300E, about that issue. I didnt believe him until my cousin ran into the problem with his 95' 500SL. It doesn't seem like a big deal, but it can possibly damage other electronics in your benz that require a certain amount of energy.

I would definitly look into that Cigar Havana...

Peace!
dj cee

__________________
http://img158.echo.cx/img158/9830/mbsig5jb.jpg

In Trance We Trust...

www.tranceaddict.com

Yours Truly,
DJ Cee

One other little thing: Check that your trunk light goes out. Switch goes bad and kills battery in one to two days. Nasty little bug to find. I found mine when I was checking my trunk seal for water leaks.

The old battery was interstate brand, and the new battery brand is a Canadian Tire battery, 850 cca.

The trunk light would not run the battery down when the engine is running 2,000 rpm at 100 KPH.

I noticed there was a bulge in the big wire leading from the alternator. I am thinking about slicing open the the insulation and examining the metal. Does anyone have a any ideas why the wire would have a bulge?

I have a new rebuilt alternator from NAPA. I'm thinking the old alternator could be breaking down under heat and therefore a simple test at the store would not show the defect.

I'll check the brushes on the old one.

__________________
1989 420 SEL

Yes, the battery goes dead while driving the car. The battery was brand new, fully charged, and 100 KM into a trip, while traveling at 100 KPH, the tape player turned off automatically, the heater fan slowed down, so I turned off all electrics, except the lights (it was night). Driver's seat heater was on low when the tape player stopped. I made it about 40 KM to a gas station, and the battery was practically dead, where the battery was recharged.

The bulge in the wire is about 6-8 inches from the alternator.

__________________
1989 420 SEL

You still haven't told us what your charging voltage is. Try the test that LarryBible suggested earlier and post your results.

If you don't want to do Larry's test... drop a couple of fuel thinner tablets into your tank. That bulge in the wire might be an electron clot.

__________________
Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

Yes, I will do Larry's test. The car is in another city, 200 KM from where I am now, but I have the alternator with me. I'll get back there next weekend to do the test. I need to wait 7 days before the CAA (similar to AAA) membership starts, so if it stops on the highway again, on the way back, at least CAA will tow me back to Toronto for free.

I pulled the voltage regulator, and compared the brush lengths to the new voltage regulator I have, and the old brushes have only worn about 1/32". I put the new regulator into the old alternator. I'll re-install the old alterantor next weekend and report back the voltage tests.

Also bought some 4 guage wire. If there is no continuity from the cable on the positive battery post to the B+ terminal on the alterantor, I'll slice open the insulation over the bulge, in case the bulge in the wire is a break or heavily corroded. If it's a break, I'll splice in the 4 guage and tape it up. The insulation on the original wire seems to be a woven cloth, maybe cotton. Also, I'll install a new alternator belt, the old one was glazed somewhat. I'll also take a complete new alternator with me.

__________________
1989 420 SEL

Boy is that the truth, I had to learn that the hard way!!