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  #1  
Old 08-14-2012, 12:49 PM
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No charge light 1981 300sd

my electronics have been making me crazy... i made a new thread to clean up my post on what i have done and what is not working...

currently my charge light is not on with the key in the on position.. it does not come on either while the car is running... I switched the bulbs and still nothing i checked power to the back of the light and got .67 volts.

My battery light used to come on until today and now a second rebuilt alternator is not charging only seeing 5 volts at any rpms and battery was at 7 volts... I just charged my battery again....

The wires and cables are brand new 2 gauge wires and the red wires are 10gauge replacement ground strap was cleaned on the car and seemed fine my car is very clean and rust free. i also cleaned all terminals at junction box.

alternator is a 125 amps bosch reman.

glow plug relay turns on when key is on and clicks off after 30 seconds seems to be working as it should (80amp fuse strip was checked and i tighted the screws holding it)

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  #2  
Old 08-14-2012, 01:27 PM
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The brake light must illuminate when the key is in the run position. If not, either the bulb is ng or the ign switch is not supplying it power.

connect a voltmeter to pin 6 of the bulb and ground, with key in run, should see 12 v.
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  #3  
Old 08-14-2012, 01:39 PM
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Quote:
Originally Posted by funola View Post
The brake light must illuminate when the key is in the run position. If not, either the bulb is ng or the ign switch is not supplying it power.

connect a voltmeter to pin 6 of the bulb and ground, with key in run, should see 12 v.
im hitting 0 volts at pin 6... so is there a short in my blue wire also i am hitting 0 volts at the alternator where the blue wire connects to alternator with key in on position.
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  #4  
Old 08-14-2012, 01:57 PM
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Quote:
Originally Posted by ibenz View Post
im hitting 0 volts at pin 6... so is there a short in my blue wire also i am hitting 0 volts at the alternator where the blue wire connects to alternator with key in on position.
probably not a shorted blue wire which would have smoked. check if you get 12 v at fuse 12 with key in run position, if not, ign switch ng
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  #5  
Old 08-14-2012, 02:08 PM
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Quote:
Originally Posted by funola View Post
probably not a shorted blue wire which would have smoked. check if you get 12 v at fuse 12 with key in run position, if not, ign switch ng
12.45 volts at pin 12
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  #6  
Old 08-14-2012, 02:18 PM
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Quote:
Originally Posted by ibenz View Post
12.45 volts at pin 12
you mean fuse 12? then check wire from ign sw to bulb.
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  #7  
Old 08-14-2012, 02:32 PM
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Hmm

I hope you have NOT removed the cable from the battery with the engine running, that could blow the diode bridge in the alternator.

The instrument cluster charge light usually does not illuminate bright enough to see below 9.5v...

FYI; You need to read Myth #2.
Automotive mythology #101

It sounds like the alternator is bad again, and/or there is a massive draw on the system.

You need to remove the alternator and have it tested.
Recharge the battery while the alternator is out.


Here is a simple brute force diagnostic:

#1. Start the engine (keep it running).

#2. Unplug the glow plug harness from the relay.

#3. Test battery voltage, and write down the reading.

#4. Turn off the climate control.

#5. Test battery voltage, and write down the reading.

#6. If the auxiliary cooling fan is running, unplug it.

#7. Test battery voltage, and write down the reading.

#8. Open the fuse box, remove one fuse.

#9. Test battery voltage, and write down the reading.

#10. Remove one fuse.

#11. Test battery voltage, and write down the reading.

#12. Repeat step #10 and #11 until all fuses are done or voltage jumps to normal.

If no issue is found through the previous tests, my best guess is:

* An instrument cluster circuit board issue. W123: Instrument cluster Printed Circuit Board repair

* The ignition electrical switch is damaged, making/breaking connection causing persistent random voltage spikes 0v - 14.5v at the alternator. Ignition Cylinder Tumbler replacement; mixed diesel/gas

* A broken or seriously corroded wire or connection causing persistent random voltage spikes 0v - 14.5v at the alternator.

* The starter cable has a random massive short to ground.

* The starter solenoid has internal damaged causing random massive voltage spikes.


.
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Old 08-14-2012, 02:33 PM
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Quote:
Originally Posted by funola View Post
you mean fuse 12? then check wire from ign sw to bulb.
yeah fuse 12... 12.6 volts.... how do you check it from ign to bulb... sorry im a newb at this... do i unplug the back of ign sw and do i remove bulb or just stick it in the back
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  #9  
Old 08-14-2012, 02:36 PM
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Eek

It took over an hour to assemble my answer between customers.

happy to see others may have isolated your issue.

.
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  #10  
Old 08-14-2012, 02:36 PM
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Quote:
Originally Posted by whunter View Post
I hope you have NOT removed the cable from the battery with the engine running, that could blow the diode bridge in the alternator.

The instrument cluster charge light usually does not illuminate bright enough to see below 9.5v...

FYI; You need to read Myth #2.
Automotive mythology #101

It sounds like the alternator is bad again, and/or there is a massive draw on the system.

You need to remove the alternator and have it tested.
Recharge the battery while the alternator is out.


Here is a simple brute force diagnostic:

#1. Start the engine (keep it running).

#2. Unplug the glow plug harness from the relay.

#3. Test battery voltage, and write down the reading.

#4. Turn off the climate control.

#5. Test battery voltage, and write down the reading.

#6. If the auxiliary cooling fan is running, unplug it.

#7. Test battery voltage, and write down the reading.

#8. Open the fuse box, remove one fuse.

#9. Test battery voltage, and write down the reading.

#10. Remove one fuse.

#11. Test battery voltage, and write down the reading.

#12. Repeat step #10 and #11 until all fuses are done or voltage jumps to normal.

If no issue is found through the previous tests, my best guess is:

* An instrument cluster circuit board issue. W123: Instrument cluster Printed Circuit Board repair

* The ignition electrical switch is damaged, making/breaking connection causing persistent random voltage spikes 0v - 14.5v at the alternator. Ignition Cylinder Tumbler replacement; mixed diesel/gas

* A broken or seriously corroded wire or connection causing persistent random voltage spikes 0v - 14.5v at the alternator.

* The starter cable has a random massive short to ground.

* The starter solenoid has internal damaged causing random massive voltage spikes.


.
ok i will try this... all these problems started after i installed a new ac system and i have never taken off a battery cable while running... i always disconnect it when doing anything... also my ignition switch assembly is entirely brand new unit... i will post what i find with the fuses...
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  #11  
Old 08-14-2012, 03:40 PM
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Quote:
Originally Posted by ibenz View Post
yeah fuse 12... 12.6 volts.... how do you check it from ign to bulb... sorry im a newb at this... do i unplug the back of ign sw and do i remove bulb or just stick it in the back
Look at a wiring diagram. identify where the parts are and have at it.
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83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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  #12  
Old 08-14-2012, 03:43 PM
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i just had the alternator tested again and it failed... they said the voltage regulator was out... Is there something in my car that would cause this to happen twice.. or is it just crappy reman parts that is the problem... once i get the new one in i will test all the fuses and see if something is running too high...
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  #13  
Old 08-15-2012, 09:49 AM
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Quote:
Originally Posted by ibenz View Post
i just had the alternator tested again and it failed... they said the voltage regulator was out... Is there something in my car that would cause this to happen twice.. or is it just crappy reman parts that is the problem... once i get the new one in i will test all the fuses and see if something is running too high...
Is this the 3rd new alternator plus the original alternator that has failed? Were they all bench tested or tested on the car?
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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked
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  #14  
Old 08-17-2012, 03:00 PM
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Yes its the Third rebuilt alternator The original that my car came with was never bench tested to find out the problem...

The first rebuilt one was not bench tested before i put it on the car... wish i had cause it didnt work at all never would charge from the start...

The second had the internal brushes fry within two days of driving.

the third had a bad regulator. (this is why my charge light was not coming on with the key in the on position)

now my fourth one is working great so far no issues at all... charge light comes on with the key on and battery is fully charged after a two hour drive.
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  #15  
Old 08-17-2012, 03:02 PM
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Quote:
Originally Posted by whunter View Post
It took over an hour to assemble my answer between customers.

happy to see others may have isolated your issue.

.
Thanks for that post hunter I checked all my fuses this morning and noticed some spiking in my AC system. The source seems to be coming from the control unit which started to turn on and off the system at random. Also there was high amperage coming from my auxiliary fan which blew two fuses... for now i have taken out my number 11 fuse and auxiliary fan fuse til i can get it replaced.

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