Alternator question., Not Charging. Options

[Olympic 914]

Took the car out for a drive today, planning on going to dinner. everything is working as it should. getting on the PA turnpike and I had to accelerate briskly to get into traffic, and a moment later I noticed that the RED alternator light had come on. Pulled of at a wide spot to check the belt and wires and shut it off. Not checking the belt with it running. Belt good, plug tight, tapped the VR a couple times for good measure and started it back up. Light still on and now my Autometer AFR gauge just had bars. I know that is because it doesn't turn on until the voltage is +13v So not charging.

Now I am on a limited access highway with the next exit `12-15 miles away. Good thing had the battery fully charged on the tender before I left the house. So I made it to the next exit, turned around and headed back home for a total of 35 miles on battery only. Whew. But that shot dinner.....



Replace the VR with another I had that previously tested good. still no charging. checked the plug on the relay plate again. looks good.

I have not yet checked the wire connections at the alternator, possibly a wire vibrated loose during the brisk acceleration.

Now the question

I read to test the VR to short between D+ and DF and if the alternator is good voltage at the battery will go to alternator maximum of about 15-16V

So do I REMOVE the VR for this test? and jump between the D+ and DF at the relay plate.
OR
Leave the VR in place and short between those pins?

[GregAmy]

That post #15 is a gem...

Camping onto this one for a slightly different problem: GEN light comes on strong with key on, engine not running, But then the GEN light glows very soft at idle, and then comes on stronger as RPMs build. Battery is getting ~13.5 volts when running.

Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator.

Check. I get around 15.5V at idle and up to 17+ as I rev it up.

To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply

Check. Same as above, 15+ V at idle and 17+ as I rev it up.

Problem is, I can't check to see if it extiguishes the GEN light, because my GEN light is not on with the voltage regulator removed. It'll only come on with the regulator installed. This makes sense, because looking at the wiring diagram the ground side of the GEN light is through the voltage regulator; it's blocked by diodes at the alternator from grounding.

Does everyone else's GEN light come on with key on and engine off when the VR is removed?

I did some further checks. Pulled the combo gauge out and measured voltage at the GEN light housing. With the engine off I'm getting 0V across the terminals, but with the engine running I'm getting ~2V at idle with the blue (D+) wire hotter than the red (system) voltage wire, rising to nearly 4V at revs. Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+.

That would certainly explain the glowing bulb.

So here's the key question: what is supposed to be at D+? I'm guessing the same as system. B+ is being regulated, so the rest of the car is getting the proper voltage, it's just the D+ wire that's too hot. Unfortunately, I don't know enough about these systems to understand why that could happen.

Since the rest of the car is not overcharging it seems safe to drive, and it'll still glow bright if I fail the alternator, but I'd prefer to not ignore it.

I REALLY don't want to replace the alternator in this thing...Thoughts appreciated.

Greg

Edit: an added data point. I swapped out the Hella solid state VR for a resgular Bosch VR of unknown provenance. Now I'm getting 13.5 on the D+ side and 12.2 on the B+ side. I might just buy a new VR from a local FLAPS and see if that resolves it.

[Spoke]

Does everyone else's GEN light come on with key on and engine off when the VR is removed?

Yes, the light is on with key on and engine not running and off with VR removed.

Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+.

That would certainly explain the glowing bulb.

I'm not sure I follow your measurements. What are the 2 measurements at S9 and D+ both to ground at the same condition with the VR installed? At idle and 2k RPM. The difference between the voltage at S9 and D+ is the voltage across the GEN light.

These 2 voltage come from the 2 steering diode pins on the alternator which derive voltage from the same stator windings. They should always be the same during operation. This could point to alternator diode issue although I wouldn't replace the alternator unless sure it's not the VR. It would be convenient to swap the VR for a known good one before buying a new VR.

So here's the key question: what is supposed to be at D+?

D+ doesn't matter in this case. D+ is the voltage across the armature to provide field current for the armature coil. It will vary with load. The VR controls this.

Since the rest of the car is not overcharging it seems safe to drive, and it'll still glow bright if I fail the alternator, but I'd prefer to not ignore it.

Agreed it should be ok as long as the battery voltage stays above 13V and below 15V.

[GregAmy]

Yes, the light is on with key on and engine not running and off with VR removed.

How? Look at the wiring diagram: if you remove the voltage regulator then to what circuit will the GEN lamp ground? The diodes in the alternator should stop it from being grounded there, leaving only the circuits in the voltage regulator...so, to the wiring diagram, the GEN light should not be on with the VR removed and the key on.

Have you observed it that way yourself? If not, give it a try.

I'm not sure I follow your measurements. What are the 2 measurements at S9 and D+ both to ground at the same condition with the VR installed?

Exactly as I wrote above: "Measured to ground, I'm getting system (~13.5V) voltage from the S9 fuse and ~15.5V at idle and ~17.5V (max alternator output) at the blue D+."

Direct to battery using the same ground is within 0.2V of S9, as measured on the S9 side of the GEN light housing.

These 2 voltage come from the 2 steering diode pins on the alternator which derive voltage from the same stator windings. They should always be the same during operation.

"Should".

Ain't.