Battery, Parking Brake, and Brake Wear Lights staying illuminated---why? - PeachParts Mercedes-Benz Forum

1983 300TD · #1 12-08-2004, 06:06 PM

Greetings Gentlemen.

The wife and I jumped in the car to run to town, and about 2 minutes after starting it, the parking brake, battery, and break wear lights all came on suddenly. Also (I forgot) the little orange low fuel indicator. Plenty of fuel in the tank, parking break wasn't on, brakes are fine, etc. So, what gives?

Alternator? Fuses? Voltage regulator? The car ran fine, and I popped the hood, both belts were in place. I noticed a decent sized nick in the back belt, but that wouldn't matter, would it? Thanks for your time and input.

Damon Fite 1983 300TD wagon---300,000miles+

WannaWagon · #2 12-08-2004, 06:12 PM

Mine has started doing that, too, on cold mornings when I first start it up and the idle is down and kinda lumpy. When I rev it up a bit, the lights go off and stay off. ???

dmorrison · #3 12-08-2004, 06:22 PM

Those items recieve their ground thru the seat belt relay unit under the dash just above the parking brake assembly. My fuel reserve light would not test even though the sender and wire worked fine. I found in my research on the light that all those units test thru the seatbelt relay.

Dave

1983 300TD · #4 12-08-2004, 06:31 PM

Is the seatbelt relay such that I can unplug it and plug it back in? Would that "reset it"?

SD Blue · #5 12-08-2004, 06:33 PM

Do you know how old your alternator is?
In both cases, it sounds like a diode just went in your alternator.
Check the voltage at the battery right after you first start it up. Should be close to 14v. (neg. to eng./ pos. to batt.)

If you get a little charge voltage, you might check the voltage regulator brushes. Disconnect the battery first . Then the regulator is held in the back of the alternator by 2 screws.

Oh BTW, check and/or clean the ground cables. Both battery-to-chassis and chassis-to-engine.

rg2098 · #6 12-08-2004, 06:43 PM

I literally just got in from replacing the alternator due to a blown diode. My symptoms were completely opposite, All my lights, execpt ironically the seat belt warning would NOT come on under any circumstance. The battery light would come on when the ignition was turned off but go off when ignition turned back on.

1983 300TD · #7 12-08-2004, 07:04 PM

Quote:

Originally Posted by SD Blue

Do you know how old your alternator is?
In both cases, it sounds like a diode just went in your alternator.
Check the voltage at the battery right after you first start it up. Should be close to 14v. (neg. to eng./ pos. to batt.)

If you get a little charge voltage, you might check the voltage regulator brushes. Disconnect the battery first . Then the regulator is held in the back of the alternator by 2 screws.

Oh BTW, check and/or clean the ground cables. Both battery-to-chassis and chassis-to-engine.

I forgot to mention that 2 or 3 times while driving (after all the lights came on), the lights went out for a couple of seconds..then came back on. Would this be consistent with a blown diode, or perhaps indicate as suggested dirty connections? When driving, none of the lights (including headlights) dimmed, radio connection was fine, everything performed as should. Does this help narrow down any conclusions? Thank you.
Damon

SD Blue · #8 12-08-2004, 07:24 PM

First time I had the symptoms of warning lights came on while driving. Tried the regulator first. No such luck. It ended up being the alternator.

Second time it was just the battery light and the other warning lights would not come on at all. Alternator again!

I am not sure why there were difference. I did not check into the wiring diagram that closely. Maybe in one instance the diode was weak and in the other it was open.

Anyway, it was the alternator both times. Bad grounding can also damage your alternator.

1983 300TD · #9 12-08-2004, 07:36 PM

So let's assume that it is the alternator, and that it needs to be replaced, what kind of a time frame am I working with? It must still be charging somewhat, shouldn't it? Are we talking days, weeks, or just whenever it decides to poop out?

boneheaddoctor · #10 12-08-2004, 09:47 PM

Quote:

Originally Posted by 1983 300TD

So let's assume that it is the alternator, and that it needs to be replaced, what kind of a time frame am I working with? It must still be charging somewhat, shouldn't it? Are we talking days, weeks, or just whenever it decides to poop out?

I had a regulator go out......twice....mine would OVERCHARGE to the tune of 17.8 volts running.....smoked a tach, stereo and half the lights on the car the first time.

KCampbell · #11 12-08-2004, 10:09 PM

Quote:

Originally Posted by 1983 300TD

So let's assume that it is the alternator, and that it needs to be replaced, what kind of a time frame am I working with? It must still be charging somewhat, shouldn't it? Are we talking days, weeks, or just whenever it decides to poop out?

It really would be a good idea to get a voltmeter on it while running, you can even stick the probes into the cigar lighter socket if you know what you're doing. If you have high output from the alternator, anything much over 15.5V, you will be frying the battery and other things before long. If you have less than 13v then you're probably not charging and it just depends on how much juice you draw before the battery won't start anymore.

If you are undercharging you could theoretically hook up a battery charger each night and keep going for quite some time, providing you don't do much driving with lights on, stereo blaring, heater fan going, etc. One of my old diesel tractors has no charging circuit anymore, I just recharge the battery every dozen starts or so.

Kevin

SD Blue · #12 12-08-2004, 11:50 PM

Quote:

Originally Posted by 1983 300TD

...... whenever it decides to poop out?

Lots of variables here. One forum member drove all the way from Alaska to Pennsylvania, I believe, without a working alternator! Daytime driving, no blower for heat, and charge it every nite. I dunno, how much do you want to put up with? If the problem is cost, you can go as long as you need to. Alternator is pretty easy to change.

dmorrison · #13 12-09-2004, 01:45 AM

By all means check your alternator. BUT, I still think its your seat belt warning relay.

Go to this page of skinnerbox. Go to "warning system" , page 120

http://skinnerbox.steaky.org/Service/W123/w123CD2/Program/ETM/123%20turbodiesel_2.pdf

Notice your brake warning indicator, and charge indicator go directly to the "warning system" also the brake wear indicator goes to the warning system thru a 10 ohm resistor and the low fuel indicator goes to the warning system thru a 18 ohm resistor.

If your seat belt warning relay goes bad, it may send voltage thru these circuits.
All the lights that came on had only one thing in common, the seat belt warning relay.

Here is the unit at Fastlane

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog2.mercedesshop.com/&cookieid=1EC03H10H1EC03H610&year=1983&make=MB&model=300-TDT-001&category=All&part=Seat+Belt+Warning+Relay

Dave

1983 300TD · #14 12-09-2004, 07:51 AM

I just want to say thanks! for all the great input and suggestions. Today, first thing, I'll get a voltmeter on the old girl and see what we got. Then I'll check all my connections, grounds, etc. I'll post my results. Thanks again.
Damon

1983 300TD · #15 12-09-2004, 05:31 PM

After starting the car this morning, and driving less than a mile, all of the lights went out. It's been fine all day, just like the car was playing a joke on me. It took it to Advance Auto for one of those free battery/alternator checks, and both were fine. The alternator was putting out 13.51 volts. So the only thing left to do is a little clean up at the alt. post, and take it from there. I think dmorrison called this one. I think my seat belt warning relay is on the brink. I'll pull that out this weekend for contact clean up and visual inspection. Thanks for all the replies!

Damon Fite ---1983 300TD Wagon 300,000miles+