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  #1  
Old 10-23-2020, 07:50 PM
WingnutWick's Avatar
WingnutWick WingnutWick is offline
 
Join Date: Jun 2013
Location: Lemoore
Posts: 208
Default EI UBG-16 RPM with toggle switch ignition

Hello,*I have a UBG-16 and an RPM module. I recently converted to toggle switches for the ignition and I am curious how to wire up the module in this instance. I have one of the pickups routed directly to the*electronic ignition RPM output with no isolator and this work fine, except*when the electronic ignition is placed off (during mag check) I lose RPM data. So I would like*to wire up the magneto that I use for the other side but I want to make sure that I am doing it correctly.*

I currently have*the mag P-lead running to a switch which will ground the mag when*closed. I was thinking of simply connecting the other pickup, with an isolator per EI instructions, to that p-lead on the switch. Will this work? Will weird things happen when the switch is closed (grounding the mag)?
I've attached a diagram of the prescribed wiring and what I am thinking.*

Thank you all!

Cheers
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  #2  
Old 10-23-2020, 10:04 PM
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Lenny Iszak Lenny Iszak is offline
 
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Yes, that looks correct.
Nothing weird will happen. The toggle switch will ground both the mag and the RPM module's input.
The isolator is there to protect the mag from being grounded by the RPM module.
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  #3  
Old 10-23-2020, 10:30 PM
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WingnutWick WingnutWick is offline
 
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Ok, that's what I figured. How does that isolator work out of curiosity in this setup. You (I) would think that if an RPM signal can go from P-Lead to the box, how does that not also ground it. I am an electrical invalid so pardon what I'm sure is an obvious answer.
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  #4  
Old 10-24-2020, 07:50 AM
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Lenny Iszak Lenny Iszak is offline
 
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Location: Palm City, FL
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The magneto p-lead can be grounded by either the ignition toggle switch or the RPM module.
The isolator is likely just a resistor. Even if you ground the p-lead through that resistor there's no significant current passing by and the mag keeps on going. Voltage still makes it through the resistor so the RPM module can measure the pulses on the p-lead.

A while ago I attached a scope to a 6 cylinder P-Mag. Check out the signal on the P-lead. It alternates between +110V and -100V. (See video below). It likely gets higher with higher RPM. That's a pretty nasty signal, so make sure the wires that carry that kind of voltage are all shielded.


https://youtu.be/66plAjpzM0c
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