Re: Mercruiser 140 ignition coil voltage
You need to be careful the 4cyl engine has specific requirements when it comes to coil resistance. In addition the Pertronix Ignitor I is different from the Ignitor II.
The Points and Condenser or Ignitor I installations require a coil with 3.0 ohms of internal resistance or you need to have either an external resistor or resistance wire upstream of the coil.
If you have a resistor the Ignitor red wire hooks to the wire feeding the resistor and the black wire hooks to the (-) side of the coil. Based on your readings it looks like you may have a coil with internal resistance but to be safe you can check it easy enough.
Check the resistance of your meter- touch the red lead to the black lead and write down the number ie .2
With all wired disconnected from the coil touch the red Lead to (+) side of coil Black lead to (-) side subtract the number above from the reading and you have your coil's resistance. Or if you can find your coil's part number see below. The coil for a 4cyl engine with no external resistor should be 3 ohms.
Flame-Thrower? (Pertronix) Coil Primary Resistance:
40001 1.5 Ω (oil-filled)
40011 1.5 Ω (oil-filled)
40111 1.5 Ω (epoxy-filled)
40501 3.0 Ω (oil-filled)
40511 3.0 Ω (oil-filled)
40611 3.0 Ω (epoxy-filled)
Do not use any other Flame-Thrower? coil, as it won't have enough primary resistance, allowing too much amperage to flow to the ignition module, destroying the module or shortening its life. (except if you have the Ignitor II)
As Fishermark stated above the red wire from the Pertronix unit/ distributor needs clean
switched 12 volt power. Be careful about hooking up to an electric choke I have heard that you could see reduced voltage during cold starts. If the power to the coil does not shut off when key is shut off you will fry the internal parts.
I know you do not have a Hot-spark but these guys do a good job explaining the whats-it and why-fors
Compatible Ignition Coils, Ballast Resistors, Hot-Spark Electronic Ignition