Need help with Electical Problem

We have a 1993 Transport, 3.8 L with strange electrical problems. Daughter complained about the brightness of the headlights surging while driving. Now, the headlights are both dim and the turn signal blink really slow (one blink about every 10 seconds.) The ABS indicator light on the dash is on and the voltmeter gauge hovers around 10V.

My first thought was the alternator so I pulled it and took it to Autozone for testing. They tested it twice and it passed both times.

The battery is about 3 months old so I haven't tested it yet but know that's an option. Both connections are clean and tight.

The single red wire to the alternator and the red wire to the plug in on the alternator (that both go to fusible link at the starter) both show 12V when the key is in the run position. The pink/white wire that goes from the instrument panel voltmeter gauge that SHOULD have 12V when the key is in the run position has 0. The 7.5amp and 15amp fuses that feed the instrument panel are good.

When I first started checking it, the battery charge was 11.5. Just to make sure the daughter could get to school, I put it on the charger overnight and it charged up. When she starts the van in the morning, it starts easy, the voltmeter shows 13-14, them drops to about 10 after less than 60 seconds of running.

So, could a bad voltmeter cause this? Does the hot wire from the voltmeter to the alternator tell the alternator to charge?

Any help appreciated.

The pink/white wire that goes from the instrument panel voltmeter gauge that SHOULD have 12V when the key is in the run position has 0.
..well..it must have 12V..this is the exciter supply, no voltage, no charge, period. The voltmeter itself is a victim, not a cause.
www.avigex.ca/xport/chargingstarting.jpg
www.avigex.ca/xport/ignitionkey.jpg

Begin with the ignition switch ..a likely suspect but ABS and pwer windows would be dead......and follow through down to alternator as necessary. DO power windows work normally?

also, try removeing the neg. batt. cable when it is running.
It should stay running. If not, I would say an alternator issue. there may be an intermitent problem internally

also, try removeing the neg. batt. cable when it is running.
It should stay running.
Yes it should....and I have done that in "controlled" conditions, but this practice is potentially dangerous ; while acceptable in good od times and tolerable if the alternator and regulator are proven good from the start , disconnecting the battery (that acts as a high load damper) with a failed regulator can let the alternator generate voltages much higher than what the electronics can sustain and create havoc in computer, radio, ignition module, sensors, etc.
IN fact, I had blown both headlights of my hellish :evillol: Taurus in one second doing just that....the computer had survived :p
So act with caution.....

OK, so I'll try a new ignition switch. I assume you mean the electrical component under the dash, not the tumbler key switch in the column?

..Well....first I'd run a separate wire from the battery + to the pinkwhite wire to energise it then run the engine and then measure voltage which should then show above 14v, just to verify that the wire lacked supply and this is the single cause.
Try to apply voltage to pinkwhite lead at the more convenient place to begin with, then getting closer and closer to the ignition switch to eliminate all possibilities that it is cut somewhere between ignition key and alternator regulator.
Run tests by testing, not by changing parts ...it is less expensive.....
Again, since pink white lead is said to be dead, did you try power windows ; if problem comes from this contact of the ignition switch, pwr windows should not run.

ANd...the location of the ignition switch....yeah..#43 on this www.avigex.ca/xport/steeringcolumn.jpg

The power windows work so I'll start with the jumper wire and see where that leads me. I'll be out of town for the weekend so will have to work on it Monday. Thanks

Now that the snow has melted and I can work on it in the drive, here's an update:
To correct something, at the alternator, the red/white wire has power to it; the brown doesn't. The diagram on-line shows the brown wire isn't used so it shouldn't have power. The diagram in the Haynes manual shows this wire comes from the guage at the dash so it should have power. Not sure which diagram is correct.
Car totally died on the daughter yesterday after all the guages going nuts--I assume electrically run and when the battery went dead, everything went out. Charged the battery overnight and while driving this morning the alternator guage sweeps back and forth from a high of about 18 to a low of about 10 in about 30 second intervals.

Thoughts? Thanks,

... the red/white wire has power to it; the brown doesn't.
That is OK. Diagram as posted is from GM '93 Transport Shop manual, not any generic manual.
since red/white is energized, the alternator is excited.
So..is there any voltage at the LARGE RED wire...at ALL times. THis is the direct connector to battery through fusible link H at starter.
http://www.avigex.ca/xport/fusiblelinkh.jpg
At least one case was reported here where corrosion on this post (atarter) was a problem.
Since you say power somes and goes, I could also suspect the alternator, when tested, would show output current for some time but cannot sustain it for a longer time in real use because of the heat that is developped. That would justify the voltage going up and down.
Manage to attach voltmeter at aalternator red post, (should read battery voltage right away) then start car: should read like >15 V consistently).
SO, if fusble link H is OK and post is free from corrosion, you have a bad alternator...which is "normal" if it is an authentic GM original POS. You had said it was tested on the bench, but in my opinion, not long enough or at a load not high enough to reveal its problem. If you can "borrow" and install one that is verified as working correctly, you could get a clean instant diagnostic.
I changed the built in regulator in mine, as well as the diode pack. A little awkward to work in...you need unsoldering and soldering back wiring with a high power solgering gun...

Well, in tracing the wiring all the way back to the starter, I learned that if the nut to the left of fusible link B in the picture above isn't there, there is nothing holding it all together and it doesn't work very well. Not sure how, but the nut was missing and the battery cable and fusible links were just resting on the post. I'm surprised it even started. So, now it's all connected again and at least at the moment the gauge reads what it should read so we'll see if that solved it. Whether that was the problem or not, it obviously needed fixed.

Thanks to all who helped.