Electrical load problem

I'll add my 2 cents worth here. If your engine dies immediately when you turn on the heavy loads, it is not going to be your alternator or battery. It will be a voltage drop due to bad connections. Here's what I would check for;

Measure your battery voltage directly across the battery terminals. Note I said the terminals, not the clamps. Applies for both + and - posts. Should be about 12.5V without the engine running and 13.5 to 15 with the engine running and the charging system working.Make the same tests with heavy loads, (headlights, heater motor on). Readings should drop slightly. If you are dropping 2 volts or more, suspect the battery, but I expect this will not be the case in your situation as you can start the engine and cranking the starter is about the heaviest load you can encounter.

Measure the voltage at the common side of the ballast resistor. It should be within a volt of the battery voltage. Keep in mind I'm talking about the common side, the one connected to ignition power, not the single wires connected to the coil or pin 3 of the ignition module. Also, make sure the case of the module is electrically well connected to the chassis of the car. Test by measuring voltage from the - battery terminal to the case of the ignition module. Should be 0 volts. If anything does not measure up, dig out the wiring diagram and start troubleshooting. You can verify that a bad ground would be fixed by running a temporary jumber from the case of the ignition module to the battery - post. Same idea can be used to verify a problem with primary + power. Jumper the common terminals of the ballast resistor to battery + post. You will not be able to shut the car off with the key, but it should also not die when you turn on the loads.

You can find some good info at this site.
http://www.allpar.com/fix/electronic-ignition.html