No charge light but alternator is charging fine...
 

Well my electrical craziness continnues... I fixed my starter issue then my NSS went out and now speedometer and battery charge light are no longer working... its really weird that the charge light stopped working and the alternator is working perfect. I ordered a new NSS... starting to hate this car.

no, that's how the charge light is supposed to work... it comes on when the alternator is NOT working.
it's really there just to let you know when the belt breaks... most alternator failure modes do not trigger the light.

i should of said that it is with the key in the on position only when i am driving it is off also but doesnt come on with the brake sensor and glow plug light when i turn the key to the second position.

ahh.
that makes more sense.

Ive been checking my wire volts and the blue wire to terminal box is reading 1.5 volts with ignition in #2 position.

when i looked up the pin number in the dash it goes to i think either 9 or 6 in the plug. They both show 0 volts in the run position.

I also showed 6 volts at fuse 12 when grounded on either side of the fuse

I've had an interesting story with the SD. For years, it would not charge when started. The engine had to be revved to about 2K to get the brake light to extinguish. At that point, the alternator would charge. If the brake light was illuminated, the alternator would not charge.

This issue was ongoing for many years and both the alternator and the cluster were replaced during this period for other reasons. The problem remained.

I finally got off my ass today and sorted it.

The wires to the plug have the appropriate continuity. One has 12V with the keyswitch on and the other is closed to the blue wire that feeds the alternator field. So, that's good news.

The bulb is good. Excellent.

I'm thinking that the bulb is not making contact with the printed circuit board so I bend the pins slightly. No change...........no light.

After screwing with it for about an hour, I finally get a wisp of a light. The question is why?

Turns out that I can get the light to work if I manipulate the wiring bundle that goes into the plug. Interesting.

But, I determine that the plug is not the culprit because the 12V and the continuity to the alternator field is not affected by manipulating the wires into the plug. So, the plug is good. Excellent.

What is it?

Only possibility left is the sockets. They must not be making proper contact with the pins.

I carefully bend the sockets with a jewelers screwdriver to close them slightly.

I get the light to work well enough to push the cluster back in. So far...........so good.

Clearly, over time, the sockets expand and don't contact the pins satisfactorily.

I don't know of an easy solution..............the fact that the cluster was out and in at least 20 times in the past year is not helping the situation.

Thanks for that input i did what you had done with small pliers to bend it to make better contact to the circuit board... when i plugged it all back in the charge light came back on.... i would also have to rev my motor to around 1500 rpms to make the alternator excite and charge my battery...my problem has now been solved thanks to your post... and my alternator charges normally again....your the man...

Excellent. Help is what we do here!

I'll take you up on that!

For an '85 W123, I have a battery light always illuminated from start until around 1.5krpm. But at idle the voltage across terminals and from + terminal to ground is steady over 14.2V.

New flux capacitor on the alt. (I forget the name of that thing)

From what I just read, it may be the bulb / socket in the cluster, correct?

The issue has been constant since the speedo cable was replaced and engine install.

Thanks!

If battery light is working and you get 14+VDC across battery, you are usually able to get a charge. If battery light goes out when revving, I'd say you have an imbalance between the two circuits in the alternator. By Flux Capacitor I think you mean Voltage Regulator? If Reg is new then it's either poor, corroded or dirty electrical connections to alternator and/or maybe weak alternator - probably rectifiers.

Do you have an AC component in your DC voltage across the battery?

I agree. The problem is not in the gauge or the pins............the light works fine............just shouldn't be illuminating.

The problem is in the alternator or the regulator.