C123 230E Battery drain issue

[gizzardio]

Hi All

I have a C123 230E and battery was totally dead after I last drove it. I replaced it with new and then this also drained overnight so obviously there's some parasitic discharging going on with the ignition off.

Also I noticed that my dummy warning lamps do not illuminate when key is set to run position before start.


I've trawled through the forums and tried to collate all the tests recommended and the results here.

1) Test voltage across battery with engine running

12.5V - would expect 13.5 -14V here so not charging as it should.


2) Test voltage at blue wire at alternator with ignition on. Should be ~2V with warning lamps illuminated. Check also with engine running. Should be ~12V

With ignition on and connected plug, this is 10.5V without engine running. With ignition off and connected plug it remains 10.5V.
With disconnected plug, ignition on it reads 12V and with ignition off read zero.
Also above check with ground to both alternator casing and earth point.
The live + twin red wires at alternator read 12V whether ignition is on or off.

3) With ignition on, jiggle the alternator, connection plug etc to see if warning lights come on

No change


4) Check fuse 12 and voltage at either side to ground. Remove fuse 12 and check for 12V at blue wire at alternator connector or not

Either side of fuse read 12V with fuse in. Just live side read 12V with fuse out as you would expect.
Fuse still removed, no voltage at the blue wire with disconnected plug and ignition off. 10.5V at blue wire with plug connected and ignition off.


5) Check resistance / continuity of D+ (blue wire connector) through alternator, i.e. to ground

Reads 997ohms


6) Check voltage at blue wire at alternator with ignition off. Should be no voltage at all. Key on should get slightly less than battery voltage and warning lamps turned on in dashboard.

Ignition off reads 10.5V to ground. Resistance reads 538ohms between either red wire terminal and the blue wire terminal.


7) Check resistance between blue wire (with unplugged from alternator) and negative terminal of battery

Unplugged from and plugged to alternator shows infinity ohms.


8) Alternator diode test. Disconnect live + to battery. Set multimeter to diode test. Place red lead from multimeter on casing of alternator and black on post that + live was connected to. Should read about 500-800mV. Reverse the leads and should read 1 or out of range

Unplugged and using alternator terminals only. First with red lead to casing and black to + red wire terminals reads 660. Also the case for the blue wire terminal.

When reversed, red wire terminals both show 1 (out of range) but blue shows 1158. I THINK THIS IS ONE OF THE KEY TESTS HERE AS SEEMS LIKE DIODE FAILURE IN REGULATOR AT LEAST.


9) Test volt drop from alternator with black lead on + live to battery live and red lead on battery + post. Should be less than 0.2V. Can do same test for earth / ground to alternator.

Plugged to alternator, with ignition off. Was about 0.04V drop for red wire terminals and 0.9V drop for blue wire terminal. Shouldn't be any volt drop at blue wire with ignition off I would've thought as should be open circuit?


I didn't do the AC voltage test yet as I couldn't start the car after the testing and had to recharge my jump kit.


So my conclusions from above is that I at least have a problem with alternator not charging, diodes allowing current to flow from battery into alternator and out of the blue terminal to ground and wiring seems OK so far. Might not be the full story but IMO these items have be to rectified before more testing.

What you think?



AC Voltage test. Set multimeter to AC and measure across battery. This should be less than 100mV.