[Miata] 2001 won't start

[Jay Minnich]

While on the freeway in rush hour when I push the clutch  I lose  
power and the battery lite comes  on. I release clutch in a gear  
power returned-ok. Could not keep it up so stopped at side of road,  
car would crank but not start. Jump start did not help.

At garage they indicated it may be crankshaft sensor replaced but it  
tries to fire but won't stay started. I also replaced the battery  
since it was 6 yrs old. The old battery was charging

There is an aftermarket kill switch but it is de-activated.

any idea what may be wrong?