Alternator?
If its a 98 t/a still on stock alternator and battery then i'd say yeah it's pretty much shot. Mine's on the fritz too it's time for a new one but I"m going to alterstart and buying one of theirs. But it doesn't really sound like a bad batt if it happens when you hit the brake pedal, sounds like a loose ground wire or short.
Only at night...weird.
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