Hitachi 8.5" slide saw C8FB2. Wont turn off. Has brake on it to slow/stop blade when you let go of trigger. Had to unplug it. I know chit about electric motors. So is it a short? Hoping to fix by replacing the trigger, a $16 part. But should I be replacing brushes instead, first, or also?

Sounds like just the trigger switch. If the motor was shorted you would have let the magic smoke out already.
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put a new trigger in
that will probably do it

as far as brushes, how many hours on it? if it has had lots and lots of use, they might be low on life but if they need replacing, the saw usually won't run or shows signs of that as if it is a car running out of gas, so you'd know it.