Shark 18 volt vacuum will turn on, run for one second, and then turn off.
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=== Update (04/07/2019) ===
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It’s an 18 volt hand held. Shark, model SV780_N. I thought it might be a bad switch. When I took it apart, I found the switch has a circuit board attached to it. Is this some kind of overload cutout? When I jumper across the switch(bypassing the circuit board) it will keep running, meaning the battery is good.