I've had nothing but trouble with the Pertronix Ignitor II units. I've had two outright failures of the output transistor, and one have current leakage from the collector to emitter. The two failures gave no warning. The breakdown acted like a carb issue at first. It had me chasing the choke and powervalve circuits, as it was very hard to start to warm. By the way, this is on a '64.5 Mustang with a 260 v8, converted to alt. After checking all the potential fuel delivery concerns, I backed up to the ignition, only to find the dwell was too long, current and voltage to the primary was low, and my secondary voltage was only 3-4k at the coil. Pertronix was quick to replace the unit each time (lifetime warranty), and each time the failure analysis report that came back indicated that the output transistor failed due to lack of proper grounding... So, I photoed all of my connections and installation, along with recordings made with a PICO scope of voltage drop across each circuit and current flow (inductive probe), in conjunction with secondary voltage readings. After the third failure, I simply requested a refund, with which they eventually complied. I've since converted to small cap DuraSpark dizzy, wired to a GM HEI module, mounted on the bottom back of the air cleaner, to both hide it and keep it cool. i haven't had a failure yet, but its only been about a year and about 1k miles, vs six years and 5k miles with the three failures of the Ign IIs.