Electrical Mystery

This problem has me stumped (and stranded in Reseda.) Mechanic's looking at it tomorrow morning anyway, but I thought I'd throw this out
here as a sort of a Car Talk gedankenexperiment.
A few days ago the left headlight started acting flaky, randomly going out on normal beam but always okay on high beam. Probably a loose connection, but I hadn't gotten around to checking it.
Drove four hundred miles down to Los Angeles without incident, and then around town all weekend. On my way back this afternoon in moderate rain and heavy traffic, the OEM Clarion radio's audio cut out, although the display was still on. Shortly thereafter, the LCD display and separate EQ unit started flickering, but the backlight remained steady. Very shortly after that, the engine stuttered and stalled out. Not enough juice for the starter to even try to crank. A jumpstart worked, but the engine only ran for a minute or two after the donor was disconnected. The charge light never came on throughout all of this. The battery and alternator are both brand new, and the belts are fine. I disconnected the left headlamp on the chance that it was causing a short, but that didn't help.
Clearly there's a short somewhere, maybe caused by the wet weather, but what could be shorting that isn't protected by a fuse? I know a burnt-out charge light will interrupt the charging circuit, but that wouldn't account for the radio symptoms. The headlight issue seems probably unrelated. There's no visible water leak into the engine compartment, except maybe into the ventilation system's fresh-air intake door (but the air conditioning was off -- actually, it's been drained and I've pulled the compressor out altogether, so...)
Any ideas? The garage AAA towed it to is just some random place with no particular Saab experience, so maybe they (and I) would benefit from informed suggestions.
Thanks, Ludwig 1990 C900T
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Sounds like an earthing and/or short cct to me. I guess your mechanic will check your earth straps - I had one on my C900 that looked OK, but virtually fell apart when I took hold of it. I guess it wasn't a critical one though, as no symptoms elsewhere...

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Ludwig wrote:

Actually it's more likely there's an 'open' not a short.
Graham
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Along with checking for shorts, make sure the battery charging circuit is working. There is a charging lamp in the instrument cluster and if that's blown, you won't get any battery charging. If it's the wrong rating you will get some charging but not optimal, or the regulator might not kick in if it doesn't see enough of a voltage differential.
Craig.
--
Craig's Saab C900 Page at | Craig's Classic Saab Workshop - Sydney .au
http://lios.apana.org.au/~c900 | http://www.classicsaab.net and other URL's
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when you jumped it, was the negative jumper cable connected to the engine block as per instructions, or to the battery negative?
It may be that the negative cable from the alternator to the engine block was not reattached. my best guess. Who replaced the alternator?
KeithG
Ludwig wrote:

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Just to update, random mechanic didn't find any problem, since it started right up for him in the morning. (Which didn't stop him charging me $65.) The problem turned out to be a break in the alternator grounding wire right at the crimp. The ends were still sorta touching, thus the intermittency. Charge went out again at 3AM halfway up to SF, I coasted down an offramp, opened the hood, and saw it immediately -- the arcing from the semi-open had melted the wire's insulation. Fortunately there was enough spare length to cut off the melted end, strip off an inch of insulation, and wrap the bare wire around the ground post.
Lessons learned: 1) Always bring your cell phone charger when you travel, even if you think it's just a day trip. If the phone had been working I would have found the Saab specialist a few blocks from random mechanic's 76 station. 2) Avoid random mechanics. 3) Keep a decently stocked toolbox in the trunk; I was lucky this time that this was fixable with nothing but a knife and a Leatherman. 4) Road flares are a lot more fun than plastic reflecty things. Okay, I knew that one already.
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