Ignition system voltage puzzle

[pschauss]

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?

[Tony Meola]

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.

[Bruce]

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.

[pschauss]

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.

[pschauss]

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

It only took me four years to figure it out.

[Tony Meola]

Peter

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