The most stressful time on an HEI system is cold weather cranking when the engine might be turning slower than normal. A HEI coil primary has around 1/2 Ohm of resistance, so the initial surge current in the primary winding will be somewhere in the 20 amp range or so. Once the inductive reactance of the primary develops, the primary current will drop a bunch each time the module closes the circuit. The primary circuit needs to be sized to handle that surge current, so a relay would be a god idea. I've started using 60 amp Bosch type relays instead of 30, not because most circuits need the extra amperage but just because the connectors that come with the relays have bigger wires. The cost isn't that much more for the bigger relays.
Jerry
