Flaky charging system issue in 89 P/U

1989 P/U, 2WD, Carbureted, 4 speed manual. California Model.
I've got an intermittent charging system problem. It usually happens
after/during a good rain. It's definitely the alternator not switching on. I pulled the main lead going to the battery, put a volt meter between it and the positive side of the battery to bypass any short. I grounded the F terminal to switch on the alternator and bypass the regulator. No go. No charge. The alternator isn't kicking in. The engine is spinning faster. When it does kick in, the engine RPM goes down a little under the load. So, alternator suspect. Here's the thing: I have had the alternator checked twice and it's within spec.
So, I did some studying and took some readings. Here's what I got:
At the alternator 3 wire plug, there is 12.5V going to the S (voltage sensor on regulator) and L (load, iirc) terminals. There's about 3.8V going to the IG terminal. Across the 7.5 amp fuse labeled CHARGE, it also reads 3.8V. The electric choke heating coil (at least that's what the wiring diagram is calling it and it is going to the carb/aircleaner) is also on that circuit, from what I've read on the wiring diagram. I went through the wiring and traced a ~1V drop back to the engine side of the connector that goes to the choke heater (~11.8V). It should read about 12.6V as it goes straight back to the battery. So, I'd imagine there's a short in the circuit. Of course, after I wiggled wires while I was connecting and disconnecting stuff, the voltage jumped up to 12.6V at the terminal and IG jumped up to 4.5V and the alternator now kicks in. If I disconnect the choke heater coil, the voltage at IG kicks up to ~11.8V because the choke heater coil is now out of the circuit. Still, the alternator doesn't kick in. So, I assume that you're supposed to be reading about 4.5V at IG. Argh. Assumptions.
Hypothesis 1: Intermittent short in circuit containing the alternator IG terminal and the choke heating coil, causing drop in voltage in circuit. The IC in the regulator probably senses a voltage range and 3.8V is below its range to tell it that the ignition is on. So, the IC doesn't trip the proper transistor that sends current to the alternator rotor coil, even through it's getting a good 12.6V at the S/sensor terminal because it doesn't "think" the ignition is on at all.
Hypothesis 2: Although the voltage is a little low due to an intermittent short, the regulator is slightly defective or just going bad and should be sensing 3.8V and sending current to the ignition coil or something down those lines.
So, on the wiring side, trace back wires to fuse box, strip off wiring loom tape if needed, find short or excess resistance in a connection and fix. On the regulator side...um, give it a stiff kick in the teeth?
Am I barking up the right tree?
TIA.
-Beth
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I have a copy of the SecuriKey+ Programming and Troubleshooting Manual. If you still need it I can scan it and email it to you.
Does anyone out there have the operating instruction for this security system?
Paul Phoenix, AZ

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I have a copy of the SecuriKey+ Programming and Troubleshooting Manual. If you still need it I can scan it and email it to you.
Does anyone out there have the operating instruction for this security system?
Paul Phoenix, AZ

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Beth wrote:

[snip]
oops. i mean AMMETER. duh. checking for current flow.
-Beth
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Beth wrote:

THis is by far the most likely cause, especially if the alternator is original. Had a similar issue with my 89 V6, the easy test was to disconnect the battery (which can also act as a voltage regulator) while the engine was running. Everything goes dark: regulator. If, instead, the lights start cycling dim/bright, probably a wiring issue.
lycka till! GTr
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gregory trimper wrote:

thanks. :) btw, it was the L terminal that is getting the low voltage, which is connected to the charge lamp, the choke heater coil, etc. i think it's wiring _and_ possibly a flaky regulator. if it wasn't so damn windy out, i'd go work on it. frickin' vehicle. i love it but this is driving me nuts.
-Beth
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On Thu, 19 Feb 2004 20:07:05 GMT, gregory trimper

Kids, DO NOT try that at home!! Don't EVER disconnect the battery on purpose while the engine is running, the alternator can surge WAY above 13.8V and start blowing out lots of very expensive stuff - like the ECU, the fuel pump, the radiator fan, the heater fan, all the lights...
--<< Bruce >>--
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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Bruce L. Bergman wrote:

well with a 22R he doesn't have a ECU, electric fuel pump, nor radiator fan :-) At least my 85 22R non-California model doesn't.
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wrote:

I know that - but the other people who are reading this may have those (and many other) expensive parts to blow up, and they are the ones my comments were aimed at.
Heck, just blowing out the ignitor module will ruin your whole day, and put a nice little dent in your bank balance for repairs. And I know it has one of those...
--<< Bruce >>--
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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Bruce L. Bergman wrote:

Theory and practice. Yes, in theory, there can be a sudden surge in voltage with the loss of the load, which then might, possibly, cause other damage. However, in practice, extremely unlikely and a field-proven technique.
Only take risks with which you feel comfortable, of course.
GTr
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If you have close to 100K on it the alternator brushes may be worn out. This will cause intermittent charging and other flaky stuff. I think you can buy just a set of new brushes for about $10 - $20 and see if that fixes it. It worked for my 84 Truck and I put another 170K (it was at about 90K) with no further issues.
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-WJB


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Jeff Bertrand wrote:

thanks for the info. after thinking about the symptoms over, it sounds more and more like either alternator brushes or a flaky regulator. the voltage at L shouldn't really have any effect on the regulator sensing voltage and turning on/off the rotor in the alternator. now, if it was a voltage drop at S, i'd be worried about a short.
-Beth
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