Electrical issues, bad ground? loose connection?

[Motro Mofo]

Gas is too freakin expensive!!!

So, I finally decided it was time to ressurect my 1990 Geo Metro. I put new piston rings in, replaced the tranny, all filters, battery, plugs and wires, etc. etc. I am having the same problem I had before I fixed it up. The battery light comes on intermittantly. When it does, I have about 2 hours worth of driving before the battery goes dead. It seems to happen when I hit a bump or pothole. I have had the alternator tested, it came out great. I have also tested the battery,(its brand new anyways) its good. I am assuming that the problems is due to a bad ground or loose connection somewhere. I am wondering if anyone has any suggestions on locating the problem? I've tried pulling different fuses and starting the car to see if I could locate the faulty circuit that way, no luck. How should I go about this?

ANY help or suggestions would be welcomed. Thanks

[LancasterWannaBe]

Check the connection from the alternator to the battery first.

It shouldn't be a ground problem, since the whole car is grounded. The hot (+) would be the issue. Disconnect anything that takes power while the car is off (radio, clock, ect...) Then get out there with a multi meter and check the resistance on the entire car to see if there's even a short at all (you'll need to disconnect the battery). If there is check it one circuit at a time by leaving only one fuse in the box. If that doesn't lead to something, then the short is probably before the fuse box, in which case I am surprised the car starts at all.

Having said all that (probably too much) I also need to say I'm not an electrician and I hate car electrical problems. That's just where I would start.
But good luck anyway.

[V-8Fan]

When you get the car into the failure mode (as in after hitting a pothole) then measure the voltage across the battery with the engine running. Since you've had the alternator checked and it's supposedly good, you should see about 13.8 to 14 volts DC. It could be that there is a bad or corroded connection between the alternator and the battery (I am assuming the rectifiers and voltage regulator are internal to the alternator) resulting in less than normal voltage being applied to the battery. And a bad negative battery cable could be the culprit also, or maybe it is not making a good connection to frame or the engine.