88 Camry: Intermittent Alternator with Battery, Lights, and Brake Warning Lights

Hello I've got an 88 Camry, 4 cylinders, 230k mi. It runs really well except for this alternator problem which has confounded me. The car
will run fine for anywhere from 1 minute to 2 or 3 hours with the alternator on, then the Battery, Lights, and Brake Warning lights all come on simultaneously. Then the car will run off battery and no alternator for a while before going back to normal. I can't connect the intermittentness with anything: it's TOTALLY random. Sometimes the car will start with the alternator working, sometimes it won't. If I leave it for a minute and start it up again sometimes the alternator works.
So I took the alternator into the local winchester auto and they bench tested it... as much as they wanted to sell me a new one, it was fine. My own inspection reveals healthy brushes and bearings.
The indicator lights and the intermittentness of it lead me to believe that it's a short circuit. I'm not an expert with electricity, but I've got a multi meter and more or less now how to use it. My haynes manual told me that if I put the multimeter between the negative battery cable and the negative battery post while the car is turned off, there should be no voltage. There is consistantly 11.5 (my poor battery). So I pulled out every fuse, trying to get the voltage to stop. Nothing. Does anybody have any advice or resources on how to troubleshoot this beast?
Please respond by post rather than email
Thanks Dub
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If you really have 11.5 volts between the negative battery cable connector and the negative battery post, the cable is not electrically connected to the battery. As your manual states, the voltage should be 0. You need to remove both battery connectors, clean the connectors and battery posts, apply some grease, and reconnect. You have intermittent battery cable contact causing your problem based on your description.
Let the group know how it went and if this was the problem.

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dub wrote:

Follow Phil's advice in his post and while you have cables off check for continuity and resistance. You may have corrosion built up under the insulation causing high resistance or broken wire(s) in the ground cable. I've seen neglected cables have the white powder corrosion built up, under the insulation at the ends, so bad the cables had to be replaced. HTH, davidj92
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