82 240D Electrical Help Needed (GP/ALT) - PeachParts Mercedes-Benz Forum

holtonmusicman · #1 10-27-2010, 12:13 AM

My 1982 240D (480,000 miles) has a (now) recurring electrical problem.

With no warning the GP light quit glowing and the Battery light remains on AFTER the vehicle has been shut off. (these happened simultaneously so they are connected and/or related)

The last time this happened (about six months ago) I determined it was the ignition switch. I replaced the switch with a cheapo (that lasted about one month) when the same symptoms reappeared.

I replaced that switch with a better brand (Beck) which fixed it and had no other problems until late last week - when the same symptoms re-appeared.

I ordered a replacement switch and installed it tonight and the same symptoms remain.

I unplugged the electrical connections at the back of the alternator and the light goes out.

I believe the only electrical connections to the Battery Light are from either the alternator connection or the ignition switch.

This car was very well maintained before I got it (well maintained since) but it IS nearly 30 years old. I cannot find a problem with any of the electrical connections (wiring/fuses/etc) and am completely stumped.

The vehicle starts (long cranking as temps are 40's here) and it runs flawlessly.

I have been undoing the negative cable when I stop the vehicle so I don't run down the battery. Frustrated and Upset . . . it seems it's a non-stop series of problems with this car since I've had it (sigh)

Ideas/Suggestions/Similar situations.

(Things I have checked)

The GP Relay functions as I "jumped it" to check
The GP's are working fine.
Alternator is less than six months old
Wiring under dash to (and from) the ignition switch plug/loom
Wiring under hood.

vstech · #2 10-27-2010, 01:05 AM

voltage at the battery terminal?
voltage with the glow plugs on?
voltage with the engine running?

holtonmusicman · #3 10-27-2010, 07:59 AM

I appreciate the help. I don't believe any of those would cause the battery light to remain on once the vehicle is not running and the key is removed .

The battery maintains 14.7 volts

I didn't check the voltage at the GP/s because I jumped the GP relay to make sure it was functional

This is not a battery problem, or voltage problem.

I did also removed the ignition switch plug with the battery battery still connected (yeah I know) for diagnostic purposes and the battery light remained on with nothing plugged into the back of the ignition switch.

COULD a bad lead from (or to) the alternator cause a problem with the GP relay?

vstech · #4 10-27-2010, 08:32 AM

the batt light will come on when there is power to the alt, and the output is not higher than the battery power. so, a bad or corroded ground will cause the batt light to light, a bad alternator will cause the light to light.

micalk · #5 10-27-2010, 10:24 AM

But not when the key is removed from the ignition, unless....

I think you may have mis-wired your ignition switch or it is probably more likely that you have a shorted wire somewhere. The two circuits share the same wire that goes to the hot side of Fuse 12 from contact 15 (Circuit 15) on the ignition switch . Check that circuit with the ignition OFF. (Do your windows work with the ignition off?) It should not have any voltage. If that line has been connected to the battery or some other 'always hot' circuit, then it might display the symptoms you note. Your glow plug relay would always have a "RUN" signal, and may only reset and actually start glowing when cranking. It would also begin a glow cycle when you attach ground. Try attaching the ground with the ignition in the RUN position, and see if the glow light comes on.

Diesel911 · #6 10-27-2010, 10:47 AM

I think it is odd that you are getting 14.7 Volts when most of use are lucky if we are getting 13.5-13.7 Volts; if you get a little bit more than the 14.7 volts on most Cars that would be considered overcharging.

If it turns out you cannot find the issue I would consider having the Alternator tested by a shop that has a scope that can show the wave form. That would tell you if there is an internal issueinside of the Alternator. Or just exchange the Alternator.

holtonmusicman · #7 10-27-2010, 01:57 PM

I meant 13.7 volts not 14.7.

holtonmusicman · #8 10-27-2010, 07:11 PM

Problem "Solved" . . .

It is the Alternator (less than three stinking months old). It was a remanufactured Bosch unit (65 amp) from an e-bay company called Eagle Auto Electric out of California.

Anyone else dealt with these guys? The only reason I used them was because it was a reman Bosch unit and not an aftermarket.

Between Ignition Switches and Alternators I can't win for losing!

micalk · #9 10-28-2010, 09:48 AM

Quote:

Originally Posted by holtonmusicman

Problem "Solved" . . .

It is the Alternator (less than three stinking months old). It was a remanufactured Bosch unit (65 amp) from an e-bay company called Eagle Auto Electric out of California.

How does that account for the alternator light being on when the ignition is off?

Mark DiSilvestro · #10 10-28-2010, 10:00 AM

Quote:

Originally Posted by micalk

How does that account for the alternator light being on when the ignition is off?

I believe a failed alternator diode can cause the light to stay on with the key off. In my case, with the faulty brush-alignment, the light would go on and off at random accompanied by a loss of charging, but didn't stay on with the key off.

Happy Motoring, Mark

qwerty · #11 10-28-2010, 10:29 AM

Quote:

Originally Posted by holtonmusicman

It is the Alternator (less than three stinking months old). It was a remanufactured Bosch unit (65 amp) from an e-bay company called Eagle Auto Electric out of California.

I think it's fair to say that, at the prices they charge, it's not possible that you are getting a "quality" overhaul. More likely, you area getting a "working when removed" unit with a fresh coat of paint.

layback40 · #12 10-27-2010, 07:19 PM

make sure you dont have a bundle of keys hanging on the ignition switch.

Mark DiSilvestro · #13 10-27-2010, 09:04 PM

Quote:

Originally Posted by layback40

make sure you dont have a bundle of keys hanging on the ignition switch.

That would tend to wear the lock-key/cylinder - not the switch.

Early this year I had a 'rebuilt' alternator from Pep-Boys fail on my '82 240D after a few months. Turns out the rebuilder didn't get the armature contact-rings to properly align with the regulator brushes so the charge-lamp started coming on intermittently. But of course, when I tried to return it to Pep-Boys, it tested just fine!
Since then, a used alternator provided by my friend Chuck Taylor has been working perfectly.

Happy Motoring, Mark

vstech · #14 10-28-2010, 10:24 AM

yup. a really bad alternator will not only keep the batt light on with the key off, it can actually start the car on some vehicles. at a minimum, it will drain the battery in a very short time. can start fires or melt wires feeding the battery from the alt...