Charging Light W124
 

Why doesn't the charge light illuminate when the voltage regulator dies? More exactly the brushes are worn so the alternator is not charging the battery. Shouldn't the light warn of this condition?

The light comes on when the engine is not running and the key in the on position so the bulb is not burned out. The light extinguishes when the engine starts and runs.

Battery voltage is about 12 when the engine is not running. Engine running, the voltage is about 11.5. Engine running and headlights on, the voltage is about 10.5. Obviously not charging. Pulled the regulator and brushes are almost gone (many thanks to all the previous threads and all who have gone before). The OVP Relay fuse is OK.

The old threads mention charging system failures and the dash light not glowing. How can this be? I thought when the battery voltage was higher than the alternator voltage the light came on:confused:

True, and true. If the alternator is hooked up and not operating properly it should, but the lack of connection between the voltage regulator and the armature somehow doesn't pop the light.

Been there done that, happened to other cars I had with similar Bosch alternators from that era also.

Teutonic Irony
 

Jeff,
Thanks for the confirmation. I still can't understand why it doesn't trip the light. If low voltage out of the altenator doesn't illuminate the light, what does?

Is this some kind of Teutonic irony? The bulb does not show a charging system failure, but if the bulb is bad the charging system fails!

At least with Lucas stuff, the charge light means something even though it comes on frequently!
Thanks again
Peter

I don't believe that a light failure will prevent proper charging in the 124s, that is an older system.

The charge light will tell you if the voltage at the excite/armature is less than the battery voltage, which would indicate that there is no charging output. Since some failures will still have proper voltage at this internal point, but proper voltage/current won't be produced through the field winding or through the diode trio, the charge light is not fail-safe.

Not a perfect system, "idiot" lights never are, ... but some here complain that there is an oil pressure gauge and no oil pressure idiot light, ... can't please everyone.