Multiple Warning Lights; Not Alternator?

[Youngan]

1989 2WD Van.

My Oil, Charge, and Radiator warning lights are on. Alternator is charging properly (about 14.4 volts). I know that all of these lights being on is usually a sign of a bad alternator, but I’m wondering what else it could be.

A little history:

Several years ago, all three of these lights started coming on intermittently. Using a voltmeter, I determined that when these lights were on, the alternator was not putting out a charging current (voltage was below the resting battery voltage). I replaced the regulator portion of the alternator, and the problem went away.

Fast forward a few years, and the intermittent warning light issue comes back, but this time, the alternator is still putting out good charging voltage while they are on. I live with it that way for years, though the lights are on more and more often as time goes by.

Then one day this past winter, my battery is too low to start the car. I get it jumped, and check the voltage with it running. Now it’s occasionally (though not always) failing to charge when the warning lights are on. So I installed a new alternator, as I could no longer source a regulator. It works great, and the lights stay out.

Now, a few months later, the lights are on again, this time all the time. It’s still charging great.

Any thoughts on what is causing this?

Thanks
Andy

[Jan-Willem]

Have you checked if the three wires of your alternator harnas are okay? There is a three pin-plug on your alternator, and then short wire, then the same three pin plug, if you unplug it on both sides, and check for proper continuity with your multimeter. It is like a 2 feet cable, and mine had so many repairs.... I would suspect the yellow wire to be broken, and this could be further up in the wiring harness, but I think this alternator wire is an easy way to start.

[Youngan]

Thanks; that did give me somewhere to start. Unfortunately, it didnÂ’t turn up a cause, but I did get some more data.

I removed that short harness and tested continuity between the ends of each of the three wires, while bending, twisting, and tugging on the harness. Good continuity was observed on all three wires at all times. All of the connectors appeared clean and tight.

When I reinstalled the harness, I did some voltage tests:

At alternator plug, with the plug disconnected-
Key Off: yellow ~0 volts, white 12.2 volts, black/yellow ~0 volts
Key On: yellow 12.2 volts, white 12.2 volts, black/yellow 11.7 volts

At wire going plug at upper end of harness, with alternator plug connected-
Key Off: yellow ~0 volts
Key On: yellow 0.8 volts
Engine Running 2.8 volts
(in this test I only checked the yellow wire, and did so by poking through the insulation)

According to the wiring diagram IÂ’m using (which is for a 1985, not a 1989) the white and black/yellow wires come from the battery; the white one directly, and black/yellow via a relay, so their readings make sense to me. The yellow wire comes from the ECU, so could be anything; I donÂ’t know what itÂ’s supposed to be. Does anyone know if the readings IÂ’m getting seem correct? Anyone know if the wiring differs in this area on the 1989 vs 1985?

[Jan-Willem]

This is generic info, not van specific, so someone please correct me if I am wrong.

The sense wire does indeed go directly to the battery, so the voltage should equal the battery voltage, always, regardless of the posistion of the key.
the ignition wire, goes to the ignition relay, so it is live, with the key in 'run' so it should be about 12 volts, when not running, 13-14 volts when running.
the L wire, which is the yellow wire in your diagram is the Lamp wire.

as far as I know it works like this: on your dash there is a bulb with the battery icon. this should be an incandescent 12v bulb. One wire of the bulb is connected to the ignition relay, the other side is connected to the lamp connection of the alternator. (and in case of the van, this wire also goes to the computer)
So... when everything is off, both sides of this bulb have 0V
With the ignition relay on (so key in run position) one wire of the bulb gets 12v. If the alternator is not spinning/producing power, the other wire of the bulb has got 0v. One side 12v, other side 0v, so the light comes on.
If the alternator is spinning/producing power, both wires of the bulb have got about 12-14v so the light does not come on.

"yellow wire- Engine Running 2.8 volts"
So if you measure 2.8v, assuming all of the wires are intact, and the lamp is a functioning incandescent bulb, one side has 12v and the other side has 2.8v, your charging warning lamp should be lit, as it 'senses' your alternator only outputs 2.8v

the voltages you measure with the disconnected plug sound fine to me.

I put a copy of the 1987 van user manual on my google drive, I hope this link works: https://drive.google.com/file/d/1b8y...ew?usp=sharing
although I think this bit of the wiring is probably the same

[Youngan]

Thanks for that wiring diagram. As it turns out, it differs significantly from the 1985 diagram that I have as far as the charging circuit goes.

Does anybody have a diagram for a 1989? I figure I best look at the correct year, in case it is different yet again.

If your basic theory of the light operation is correct, it would indicate that there is a problem inside the alternator, in that it is not sending 12 volts (or more) to the light wire. However, since I’ve had the problem with two alternators and a third regulator, that seems unlikely. Unless something in the vehicle is causing that specific part of the alternators to fail.

[Jan-Willem]

yeah the 84 and 85 have a different engine, different steering...
I assume you would have noticed if the power steering pump is leaking all over the alternator