Laser now starts for 3 seconds then stops

[080]

I have a laser which will start for 3 seconds then stop.

I put a test light onto the negative out of the dizzy.
It lights when you turn on the ignition then sort of blinks very fast when it runs. I would not say it flashes. It looks more like an incredibly fast twinkling. Then everything just stops.

What is going on? Which one is most likely to be?

Modulator
Coil
fuel pump
fuel filter

Thanks for the help.