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oh gosh, does a distributor draw that much current? I'm especially interested in your "run-on" from the alternator! My new engine runs for just tad when I turn the key off, but the man at hotrodwires said it may be from my electric fan that was wired directly. This has been remedied since Dave Chapman put together a relay system, but I haven't started the truck since then. So would that mean most everything that draws significant current should have a relay? like my aftermarket AC system? and maybe even the headlights?
dne'
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The average current draw isn't large for HEI. But for a short time, each time the coil begins to charge, they draw a lot of current. It's called "instantaneous current draw" and it's the real reason why GM used such a large wire for HEI systems. Plenty of people have learned by experience that too small a wire diameter can cause problems with the way the truck runs.
If you had wired an electric fan directly to ignition power then the truck probably continued to run for a second or two after the key was switched off. The cooling fan motor instantly turns into a generator when you stop applying power and since there was no relay or switch, that small generator was able to supply power to the ignition system for a short period to keep it running. I'm sure Dave's relays will take care of it. Another problem that crops up is when a truck is converted to alternator. The SI style alternators in original form require a small voltage supply that's tied into the ignition wire. The factory uses a resistor or runs this wire through the ALT light to cut down on current but many people just wire it to a key on power wire during a conversion. When the key is shut off a small voltage can be supplied from this wire back into the ignition system. Some ignitions only need to see a few volts on the ign+ line to stay powered up so this setup won't shut off with the key. The relay isolates the ignition so it can't get power.
The old truck ignition switch was designed for a bit of current. Turn signals, ignition, heater fan, maybe a cigar lighter, and a tube radio might have added up to 30 or so amps. But I wouldn't subject an old switch to that kind of current draw. An underdash AC with condenser and fan can draw 10-20A alone. The electric cooling fan is probably another 15A. Any lights or other devices added to the ignition circuit only serve to route more power through your switch. A better answer if you expect to have high current draw may be to use a large relay to power a bus bar or fuse panel and tie all your circuits to that.
Headlights and brake lights are powered by battery power which doesn't go through the ign switch. But if you're planning to go with Halogen or high power lights you'll find they're brighter if you use larger wire than original. You could install relays out near the lights and get the same effect by supplying battery power through them but it seems like unnecessary complexity. Still, it may be easier than replacing all the wiring.