If you have your coil mounted in the passenger compartment, you need the Aeroflow Performance firewall feed through. These are specifically designed to ensure that the spark gets to the distributor cap instead of jumping to ground at the firewall and the voltage leaks into the passenger compartment. A 12.7mm (1/2") brass rod is surrounded by an injection mould of rynite and nylon housing to form a spark isolating path through the firewall. This feed through requires only a 25.4mm (1") diameter hole to mount directly to the firewall with high tension towers on both ends used for strong coil wire connections.