Alternator/Battery Light not coming on with ignition

[MountainD]

The battery light is not coming on when I turn the ignition to the on position and nor when I start the 1991 D110 (200TDI if that matters). I get how they work, so here is what I have checked.

The bulb is known good. With ignition off, both sides (bulb removed) have continuity to ground. With ignition on ACC (not running) I check the pad where the bulb makes contact and on one side of the pad, I am getting 12V , but I am also getting 10V on the other side of the pad (which is why the light isn't coming on at ACC)??? Shouldn't it be grounded on the other side with the ignition just on ACC but not running? I swapped alternators with a new one and I am having the same issue. When running, sometimes I am getting charge but most the time I am under 12V and draining. Something is going on. This was with two different alternators, one brand new.

I'll trace the wires, but goodness sakes, there are only three wires. Any clue what may be going on?

 

[rocky]

Are the holders contacts not making contact with the bulb any more?

 

[Napalm00]

sounds like the charge indicator wire from the alternator is having an issue of some kind. its the small brown with yellow stripe on the alternator. goes from alt>engine haness>engine to main harness connector on the engine side of the bulkhead>gauge cluster harness>indicator lamp


If i recall there also is a inline dioide somewhere up near the cluster


EDIT: do the easy stuff first and make sure you check the battery and starter connections and clean the battery /engine chasiss grounds

 

[MountainD]

Thanks--Napalm--that wire is the one I was just looking up and that helps a ton. Rocky--all good on connectors.

I hate harness issues but I'll get to the bottom of this one!

 

[Napalm00]

yup make sure to check the wiring diagram , im sure im missing some connectors/splices from memory


so you have:

Brown with yellow stripe: sense/indicator
Big brown: charge circuit
White: Tach

?

 

[RDavisinVA]

The battery light is not coming on when I turn the ignition to the on position and nor when I start the 1991 D110 (200TDI if that matters). I get how they work, so here is what I have checked.

The bulb is known good. With ignition off, both sides (bulb removed) have continuity to ground. With ignition on ACC (not running) I check the pad where the bulb makes contact and on one side of the pad, I am getting 12V , but I am also getting 10V on the other side of the pad (which is why the light isn't coming on at ACC)??? Shouldn't it be grounded on the other side with the ignition just on ACC but not running? I swapped alternators with a new one and I am having the same issue. When running, sometimes I am getting charge but most the time I am under 12V and draining. Something is going on. This was with two different alternators, one brand new.

I'll trace the wires, but goodness sakes, there are only three wires. Any clue what may be going on?

So the way the ignition warning light works is when the key is switched on electrons flow from the (+) white circuit via the IG SW that is attached to one side making the bulb filament glow because the other side is attached to the alternator field (+) brown with yellow.
This is the condition you describe with the 12V and 10V difference, but not why the light is not coming on, in fact it is the exact condition that makes the light come on. Neither side of the warning light is grounded. Not sure what you mean regarding 3 wires.

When the engine is started, the alternator starts producing (+) current of equal voltage to the (+) current that the white circuit has and this makes the ignition warning light bulb filament stop glowing.
This is how the warning light works with a healthy alternator.

With an unhealthy alternator the ignition warning light stays on or will glow dim or intermittently when the engine is running.
With a bad alternator field the ignition warning light will never come on also never coming on can indicate a burned out bulb, circuit failure, or burned out alternator diodes.

 

[MountainD]

So the way the ignition warning light works is when the key is switched on electrons flow from the (+) white circuit via the IG SW that is attached to one side making the bulb filament glow because the other side is attached to the alternator field (+) brown with yellow.
This is the condition you describe with the 12V and 10V difference, but not why the light is not coming on, in fact it is the exact condition that makes the light come on. Neither side of the warning light is grounded. Not sure what you mean regarding 3 wires.

When the engine is started, the alternator starts producing (+) current of equal voltage to the (+) current that the white circuit has and this makes the ignition warning light bulb filament stop glowing.
This is how the warning light works with a healthy alternator.

With an unhealthy alternator the ignition warning light stays on or will glow dim or intermittently when the engine is running.
With a bad alternator field the ignition warning light will never come on also never coming on can indicate a burned out bulb, circuit failure, or burned out alternator diodes.

By three wires I meant Tach, D+ and battery. Actually there are two additional all brown wires also attached at battery post (see pick). Just rechecked voltages and it is 12.2 vs 11.7. I disconnected brown/yellow from D+ post and grounded it and light comes on. Must have a bad new alternator regulator is my best guess. Should there be any direct ground to alternator? I don’t see one other than bolted to grounded engine. I’m gonna check all grounds but when I jumper the alternator case to battery, light still doesn’t come on.

 

[RDavisinVA]

Oh I get it now, you changed subjects from the warning light to the alternator connection, so I unknowingly thought you were saying the IG warning light had 3 wires, when it is suppose to have only 2.

Something caught my immediate attention in post 7: "I disconnected brown/yellow from D+ post and grounded it and light comes on."
If you can ground the brown with yellow field wire and the IG warning light glows, then obviously the bulb isn't burned out.
BUT
The brown with yellow field wire DOES NOT connect to D (+).
D (+) stands for Dynamo or the positive charging circuit.
If you connect it to D (+) then the alternator will not charge and the IG warning light will never come on because it has the same voltage as the white (+) IG SW circuit.
The brown with yellow (+) wire connects to the field, F for field.
Electrons flow through the IG warning light and charge up the magnetic alternator field when the key is switched on and that allows the alternator to produce electrons.

After reading this post, I think you'll realize the reason the alternator didn't work is because the field wire wasn't connected.

 

[MountainD]

Oh I get it now, you changed subjects from the warning light to the alternator connection, so I unknowingly thought you were saying the IG warning light had 3 wires, when it is suppose to have only 2.

Something caught my immediate attention in post 7: "I disconnected brown/yellow from D+ post and grounded it and light comes on."
If you can ground the brown with yellow field wire and the IG warning light glows, then obviously the bulb isn't burned out.
BUT
The brown with yellow field wire DOES NOT connect to D (+).
D (+) stands for Dynamo or the positive charging circuit.
If you connect it to D (+) then the alternator will not charge and the IG warning light will never come on because it has the same voltage as the white (+) IG SW circuit.
The brown with yellow (+) wire connects to the field, F for field.
Electrons flow through the IG warning light and charge up the magnetic alternator field when the key is switched on and that allows the alternator to produce electrons.

After reading this post, I think you'll realize the reason the alternator didn't work is because the field wire wasn't connected.

. Here are the instructions

 

[RDavisinVA]

In the world of British automobiles black is ground (-), brown is (+ not fused), purple is (+ fused), white is (+ Ignition on), green is (+ Ignition on, fused), and so on.
Likewise F is always a standard for field and D is a standard for Dynamo, and B is always a standard for battery (+ unless it is positive ground and that doesn't apply here).
BUT
What a terrible set of non-standard instructions.
It looks like these instructions are the typical explanation that is lost in the translation from a foreign language, like English to Chinese and back to English.
According to the instructions the alternator manufacturer is trying to rewrite the standard by renaming the field lug to D.
So it looks like you had the alternator connected according to these non-standard instructions, so there must be a different issue.

Could you please try a test for me?
I want to verify that the field is both isolated, not shorted, and will create a magnetic field (assuming it is not some aftermarket junk with fixed magnets).
Could you make a short basic fused connection?
The connection would run from D+ to B+ on this alternator with a 30 or 40 amp fuse in between.

If the answer is yes:
Leave the Brown with yellow disconnected.
B+ has the brown wire leads it is suppose to have.
Start the engine.
Measure the voltage at B+ (it should be about 12V or less).
Now shut the engine off.
Measure the voltage at B+ (it should be about 12V or less).
Connect B+ to D+ with a fuse in between (this is the short basic fused connection you made).
The fuse should not blow out.
If it does the alternator field if shorted.
Start the engine and rev it a few times.
Measure the voltage at B+ (it should be about 12.6V to 14.5V) when running.
Report back your findings.

 

[MountainD]

In the world of British automobiles black is ground (-), brown is (+ not fused), purple is (+ fused), white is (+ Ignition on), green is (+ Ignition on, fused), and so on.
Likewise F is always a standard for field and D is a standard for Dynamo, and B is always a standard for battery (+ unless it is positive ground and that doesn't apply here).
BUT
What a terrible set of non-standard instructions.
It looks like these instructions are the typical explanation that is lost in the translation from a foreign language, like English to Chinese and back to English.
According to the instructions the alternator manufacturer is trying to rewrite the standard by renaming the field lug to D.
So it looks like you had the alternator connected according to these non-standard instructions, so there must be a different issue.

Could you please try a test for me?
I want to verify that the field is both isolated, not shorted, and will create a magnetic field (assuming it is not some aftermarket junk with fixed magnets).
Could you make a short basic fused connection?
The connection would run from D+ to B+ on this alternator with a 30 or 40 amp fuse in between.

If the answer is yes:
Leave the Brown with yellow disconnected.
B+ has the brown wire leads it is suppose to have.
Start the engine.
Measure the voltage at B+ (it should be about 12V or less).
Now shut the engine off.
Measure the voltage at B+ (it should be about 12V or less).
Connect B+ to D+ with a fuse in between (this is the short basic fused connection you made).
The fuse should not blow out.
If it does the alternator field if shorted.
Start the engine and rev it a few times.
Measure the voltage at B+ (it should be about 12.6V to 14.5V)
Report back your findings.

Will do! I have to remove a bunch of stuff to check those because of the intake on the 200 TDai is in the way. So it’ll probably be next week as I moved into our new house yesterday . I did check all the grounds and everything is cleaned and solid.

This morning when I took it for a spin I had four charge everything working great but about 10 minutes later it’s slowly dropped off and went all the way back down to 12 V while running. Very strange. When I first turn the key before I start the car the battery light does not illuminate. Is that typical for a 200 TI? The light never comes on it’s just obviously not charging at full capacity. Should there be any additional ground wire directly to the alternator?

 

[RDavisinVA]

Explained in post 6.

 

[MountainD]

Explained in post 6.

Moving sucks! I was so tired I forgot that I already read that! I’m starting to get some rest, just a million boxes to unpack. Thanks so much.

 

[RDavisinVA]

No problem.
Moving is the busiest job on the planet.