Weird. I know on the 240 the signal that feeds the tach is the same signal that feeds the coil. The stock tach on my 240 went bye-bye before Barber so I was just looking at the wiring diagrams to put in another one.

I haven't looked at the diagrams for the 300 to see if it's the same deal. I'd think the car wouldn't run if that was the case, though, if you're not seeing anything on that wire.

Good luck.

David