what could it be?
 

so i have a 2000 honda civic ex, i recently got the ecm, elv module,wiring harness and a new fuse box put in it, everything was going perfect until two days after i was driving it and it cut off ,took a while to crank up but it did. the next day i was driving on the highway and it cut off, but all my lights and radio was still working just the car would not start back up, i took it to the shop that had did the ecm wiring harness etc to the car, they diaogstic was a bad battery and a altenator,and a throttle body(but I was drivivng the car with the check engine light on cause i knew it was the throttle body when i got a new engine in the car way before i got the wiring harness, ecm ,fuse box and elv module on the car) they where charging me 1k to fix the battery,altenator,and throttle body that they claim was the problem that cause the car to cut of on the highway.

Welcome in,sounds more like a cam position sensor to me.