8 ga might be overkill, but I suppose too much isn't necessarily a bad thing. 10 ga run through a 30/40 amp Bosch style relay is fine. The coil on some of these has an initial startup load of between 20 and 30 amps to energize and this will cause ignition switches to burn out...in fact I have one sitting in the garage that lasted for about 6 starts before it fried. You're safer using a relay and please be certain to check the size of wire going in and out of the relay. Some of those relay harnesses come to you wired with 16 ga wire and that won't be sufficient for anything but the relay's coil in this case. Pin 85 is ground for the relay's coil, pin 86 is to ignition switch (+ 12v) to activate the relay's coil, pin 30 is to 12v positive (from battery--needs to be 10 ga) and pin 87 goes out to HEI coil--also 10 ga. There may be a pin 87a in your harness but ignore this. It is for normally closed and you must wire through normally open for the relay to work correctly. You need to remove the connector clips from the harness and change to 10 ga. The replacement ignition switch I got was rated for 30 amps, but I'm going to give it some breathing room with a relay. Once the engine is running, the HEI takes much less amperage...maybe between 3 and 4.
