I have an 87 F250 with an 302. When I threw the timing light on it, my mark on the 10 BTC jumped all over the place. It went anywhere from 15 degrees both dirrections, but it spent most of its time on 10 BTC. It has new plugs, wires, cap and rotor.

 

That's because the timing is computer controlled. To read/set the timing accurately, you need to disconnect the SPOUT connector first. It's usually on a little pigtail coming off the distributor. Two wires, with a grey plastic jumper harness connecting them.

Jason

 

Thank you, that fixed it.