Great responses. I'll just add that if your ammeter is normally showing "C" or "D", something is wrong. It should only go to charge for a short time after starting, while the battery is re-charging. It might show slight discharge at idle w/ full load (headlights, brake lights, stereo, for sure if a radiator elec fan). Otherwise, it should stay about zero, so if not something is wrong, but probably unrelated to your main issue unless it indicates a constant short to ground that gets worse when you push the brake pedal.