Which power for Pertonix ignition - Mercedes-Benz Forum

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post #1 of 4 (permalink) Old 10-23-2010, 08:35 PM Thread Starter
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Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
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Which power for Pertonix ignition

I know there are several threads about retrofitting Pertronix onto vintage Mercedes, but I have a specific question I can not find.
I have a '72 280SEL4.5 that seems to have suffered ignition module failure. Voltage to the primary of the coil does not change when the points open. I am ordering the Pertronix 1885 module with the flamethrower coil. I am obviously replacing the MB module since it is bad.
Question is, the new Pertronix does not need the ballast resistor in series so the 12v power source can go straight to the + of the coil, but what do I do with the other power source to the existing module. There is the 12V from the ignitin switch which feeds through the resistor, and the 12V from the starter relay that supplies 12V bypassing the resistor during cranking. For those who have done this conversion, I assume youran the 12v from the switch to the coil, but what did you do with the 12V from the starter relay? Pertronix says not to leave the ballast resistor in the source.
Any other issues with the 1885 Pertronix swap I should be aware of?

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post #2 of 4 (permalink) Old 10-24-2010, 12:11 AM
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Make sure you are using the correct coil for your ignitor. If I remember, the series I ignitor requires the 3 ohm coil Check to be sure, don't trust my memory.

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post #3 of 4 (permalink) Old 10-27-2010, 06:37 PM Thread Starter
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Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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Got my new ignition today in the mail. Took a bit longer to install (about an hour total) because the leads supplied with the pertronix were too short to reach the coil so with a bit of splice, heat shrink and some wire loom, all was in place. The Pertronix installation says to use the 1.5ohm coil with V-8s without a ballast resistor. I have completely removed the MB black box and all ballast resistors. I am using the 12V supply from the ignition switch as power to the + of the coil as well as the Pertronix. Other Pertonix lead to the - side of the coil. Taped up the other 12V supply from the starter relay as it is no longer needed.

She fired up on the first crank. idles great and has more power. I did have to adjust the idle way down because it was very high. I think the old girl was struggling to stay running for a while with the old ignition.

Thanks for the help.
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post #4 of 4 (permalink) Old 10-28-2010, 12:31 PM
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Ign mod

Good to hear it worked out well. I used the adapter sold by Hot Spark. As far as your ignigtion module and resistor, take it out, put it on ebay or trash it you dont have to worry about it again
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