HELP on TACH install

I need help on install my tach. I can’t seem to find the “negative side of the coil” anyone know where/which color that is?

Take off the distributor cap, there are two wires you should see, there should be a + or - sign and pick the one u need. Find that wire outside the distributor in that cluster of wiring and splice it. Wouldnt the -neg. on the coil just be a ground? Not sure did it a while back.

its the blue wire on the big connector on the distributor