Does a Breakerless ignition ever require a ballast resistor?

My 91 5.8 L Ford motor on my Four Winns came stock with the Prestolite Breakerless Inductive Distributor (BID) ignition.
I'm testing the coil to address some idle issues. I may replace the coil and want to be certain that I'm getting the right one.


The book says the stock coil is a OEM 3852217 or Sierra 18-5437. Some of the pictures of those coils do say "Use with external resistor". The coil on there now is a Diamond E-035. It also says right on it "Use with external resistor".


But I have seen a lot of discussion that an external resistor is only needed for a breakerpoint ignition and that if you were upgrading from a breakerpoint ignition to a breakerless ignition the ballast resistor was NOT to be used. The mechanic that used to work on the boat says he DID add the resistor. Was that wrong?

Is testing the primary and secondary resistance using a basic Ohm meter good enough or do I need to take it to someone with an analyzer?


I got 2 ohms on the primary if I wait till it stops changing (book says 1.43 - 1.58) On the secondary I get 7.2 Kohms (book says 7.5 - 8.7)


Thanks

as a rule, the need for a resistor is determined by the coil.....if it says to use one, it will last a lot longer with the resistor in line.

As far as measuring the coil, you need an accurate ohm meter....most economical ones aren't accurate at the low end of their ranges.

If the ignition system has all the original (or equivalent) components, its best to follow the factory manual...

The coil is original but the resistor may have been added. I am trying to follow the factory manual. The ignition schematic does not specifically show a ballast resistor but would it?

This link for the coil has a dropdown the says that the 1990 and before with breakerpoint ignition uses an external resistor.

https://www.westmarine.com/buy/sierra--i-o-inboard-ignition-coils--P006_180_002_518?pCode=6936660

Mine is a 1991 with breakerless ignition, so perhaps no resistor should be used even though the coil says to use one.

I decided to make a splice with connectors that I can unplug. This way I can run the motor with the ballast resistor taken out of the circuit and then just plug it right back in and compare. I'll measure the voltage at the coil both ways and I'll do this right after starting and after running at idle for a while.

I think the ballast resistor should drop the voltage to the coil only when the motor idles, but it is only needed for breakerpoint ignition. Since mine has a BID electronic ignition it should not be needed. That is my understanding.

I'd like to hear the opinion of others with the Prestolite BID ignition.