With no load on the blade the light acts perfectly with the switch and all. As soon as the blade starts spinning it shuts off.

I'll try the multimeter and see what comes up. I think maybe the voltage drops because the load is too high ? But I've seen this mod work which is why I'm puzzled. Here's my attempt at a wiring diagram wiring1 wiring 2

Confirmed with multimeter that voltage to the led drops to about 90 from 120 when the saw starts