The ignition switch is the 'switch'. From the switch
J2 is engine run and on only when the key is in run. It has no fuse. It is not meant for heavy loads. J represents I for Ignition.
J3 is engine start and only on when the key is in start. It has no fuse. It directly supplies power to the coil during start.
View attachment 1716153180
With the MSD, power to the coil will come from the MSD orange wire in both start and run.
The MSD has a small red wire that must see some power to turn the MSD on. It can be connected to either the J2 or the J3 wire. It doesn't matter which as long as there is a connection between the two. The 1/2 ohm resistor is a good enough connection.
You can also join them together or jumper the 1/2 ohm reistor if you wish.
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It can be done as shown here
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or like this
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Note: The heavy red wire battery connection is illustrative. It does not have to be at the battery terminal. It can be at the starter relay junction. In fact on a car with an ammeter (like your '74) it may be better off connected to the alternator. However its only 1 amp/1000 rpm so don't sweat it. Just make sure its a good connection.