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Old 08-26-2019, 08:34 AM   #1
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Join Date: Oct 2018
Posts: 12
voltage regulator?

Problem: charging system failure.

1983-4 SAAB 900 Turbo

1984 wiring harness on 1983 carburated car, so some wires never match wiring codes.

Rebuilt alternator installed when generator light went on along with parking brake lamp and cessation of rev counter.

Regulator, allegedly, at fault in old alternator when tested at cheapo auto parts store in Roswell.

Drove two days (100) miles with light on while waiting for alternator to arrive from El Paso, TX, back and forth from campground.

Replaced alternator and the engine behaved fine for 30 miles, then stopped running:

+ no generator light with key on before starting
+ no rev counter
+ no ‘lights-on’ light
+ parking brake light stays on, though switch operates as it is supposed to operate
+ no juice to cigar lighter
+ oil, brake fluid lights OK
+ NO FUSES BLOWN
+ New ground cable
+ Newish ( 6 months) battery

Pulled dash, no chafed wires or obvious shorts at switches and bulbs nor broken circuit board at rev counter, the bulb to generator tell-tale OK.

B+ wire circuit to dash to alternator is without flaw. All connections at starter are snug and correct.

Replaced ignition switch.

Battery shows 12.3 volts after short period of charge via jumper cables and Known Good Battery/alternator system.

Jumped to start, generator putting out 12.2 volts at D+ terminal and 0 VOLTS at B+ terminal, before ceasing to run after a few minutes on charging system.

Key on, not running, voltage shown at D+ terminal and 0 VOLTS at B+ terminal.

Fuses and tell-tale light to generating circuit fine.


Stuck in a campground (Bottomless Lakes Campground, Roswell, NM) 20 miles outside of Roswell with no reliable Internet access (2 miles from campsite)and intermittent telephone service but ANY ADVICE WILL BE HELPFUL!

Lee Engdahl 208-293-6524
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Old 08-28-2019, 04:36 PM   #2
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Join Date: Apr 2017
Posts: 3
I think the + battery voltage should always be available at the alternator B+ terminal. Basically a wire from the battery goes to the starter and a wire from there goes to B+. With the ignition on battery voltage goes through the alternator warning light to the alternator D+ terminal. I'd start with seeing why battery voltage isn't getting to the B+.
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Old 08-28-2019, 05:38 PM   #3
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Join Date: Oct 2018
Posts: 12
Thanks Jimbab5, you're right. See below, thanks for reply.

The end of the problem

The alternator failure has a happy ending; after consultation with Marion of Marion’s Automotive in Sacramento and Jerry Danner of Mile Hi Saab in Denver both independently concluded the rebuilt alternator was bum. I had ordered a replacement from the only auto parts store in Roswell to have them on their inventory, and when it arrived on Tuesday I took a ride into Roswell from the Bottomless Lakes Campground. The second rebuilt was manufactured in Mexico, rather than the USA, and it produces 14.5 volts reliably.

Given the propensity of wiring 30 years or older to moulder, I would not have assumed the component was bad, but so it was. Since it was the only ancillary part of the car I had not rebuilt or inspected it was only right it would fail. For those of you who might have thought about the problem, thanks, and my gratitude to both Marion and Jerry: they are both first-class mechanics and decent sorts.
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Old 09-04-2019, 04:03 PM   #4
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I'm still puzzled why no voltage at the B+ terminal, even with a bad alternator. That should always be there unless the battery is completely dead.
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