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My port engine has a Prestolite IDU 7801BS electronic distributor with a Sierra 18-5433 coil. The label on the coil says it needs an external resistor.

With all of the wires connected and the ignition on I meshed 6 volts at the positive terminal on the coil. There are four wires connected to the positive terminal of the coil, three brown and one purple. When I disconnect these wires the two brown ones which share a connector show twelve volts. Can the coil and the ignition module be putting so much of a load on the circuit that the voltage is cut in half?

Peter

If Bruce does not see this and respond send him a pm. I think he would be the best one to answer that question.

Balast resistors were used in point ignition to keep the points from burning, coils lasting longer. Sometimes they were external or internal to the coil.

Electronic systems should have a full 12v feeding the system with the properly matched coil to the distributor to provide the best spark.

It sounds like you have a resistor feeding the coil + from the ignition.

By eliminating the ballast wire or resistor, you can eliminate the wire from the starter with the electronic distributor. That wire goes to the I terminal on the starter.

Unless there is a bad connection, the load should not drop the voltage down. That's what the resistor does.

I took some more measurements. If I disconnect the red wire from the ignition module in the distributor to the + terminal on the coil, I get 12 volts between that terminal and ground. With the ignition module connected, ignition on, engine not running, I get 6 volts. With the engine running it's 10 volts.

The ignition module is the Sierra 18-5239 electronic conversion kit.

Turns out it was a flaky ignition switch on the flying bridge.

It only took me four years to figure it out.

Peter

Look at it this way, it was simple. Too simple that is why you missed it. We all have overlokked the simple things.