I think these guys nailed it immediately. I've had a similar problem when my ignition box was going bad. Sometimes you can even see they look a little gooey/melted on the back when they're going bad, but it's not always visible like that.
70 Roadrunner convt. street car
440+6, NOS, 4-spd, SS springs
'96 Mustang GT convt. street car
'04 4.6 SOHC, NOS, auto, lowered
"Officer, that button is for short on-ramps"
