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Discussion Starter #1
I got a super deal on a Tach off a 1998 Harley Roadking Police bike. The bike is a single fire ignition (2 coils) just like the VN2K. However, the tach is still a dual fire (has only 3 wires), so Harley must have had an adapter in line somewhere, so I still need a single fire adapter. I see they are easy to make. Here is my question:

The diodes are necessary to keep current from the firing coil, going over to the other coil, and the resistor keeps the current at a level to keep the tach from spiking. Every schematic shows each pair of resistors and diodes twisted together...parallel. Since electricity takes the path of least resistance, why would the current not back flow through the resistor and bypass the diode all together?? Shouldn't the diode and resistor be soldered end to end (in series??)
 

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1946-2014
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When a diode is forward biased(turned on) the resistance is very low and the resistor in parallel with it is most likely a very high resistance(Megohm range), so the resistor would knock the signal down to the point it would not do any damage
 

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Discussion Starter #3 (Edited)
When a diode is forward biased(turned on) the resistance is very low and the resistor in parallel with it is most likely a very high resistance(Megohm range), so the resistor would knock the signal down to the point it would not do any damage

Thanks.

They are all showing a 100k ohm resister.

Then would having it in series hurt anything? Just seems better.
 

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1946-2014
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Yes it would hurt something. It would prevent the signal going where it needs to go when it is supposed to. It is there for a purpose, to prevent back feeding from the other coil and causing erroneous readings.
 

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Discussion Starter #5
Yes it would hurt something. It would prevent the signal going where it needs to go when it is supposed to. It is there for a purpose, to prevent back feeding from the other coil and causing erroneous readings.
Just to clarify, I meant having the diode and resistor wired in line (series)
with each other. Diode first, then resistor, on each leg, then fed to the tach signal wire. Evidently it's a moot point
 

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Discussion Starter #7
I knew what you meant. Series connection would not work because the resistor in series would block ALL signals.

So...........if I only want the tach to be non functional & ornamental only, go ahead and wire it in series then.

That about the size of it?















Thanks. Kiddin aside...I do appreciate that being cleared up
 
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