Any electronic wizards out there?

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Dec 28, 2006 | 08:02 PM

rotorwing70

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Joined: Aug 2006

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Any electronic wizards out there?

I have been tinkering around with a tach install on my 05 1200C for several days and need some input from someone with an electronics background. The tach I have is a pre-serial bus tach from a 03 Sportster. This tach requires an analog square wave signal from thecoil. These tachs were designed to be used with a dual fire ignition system like the earlier Sportsters (the pink wire setup) so when you connect them to one side a newer single fire ignition coil they read half the actual rpms. There are some "adapters" available butbeing the tight-wadI am I was thinking of a cheap dyi fix. My first thought was to simply install two leads with diodes, one each on the two negativewires leading to the two coil primarys thus combining the two signals and doubling the signal pulses to the tach. Seemed to simple so I searched the net for a couple of days and finally found a German ignition manufacturer that had an adaptor circuit diagram on their website. Their adaptor consisted of two leads with a 50V1A diodeeach. The leads wereconnected at one end to form the tach lead while the twoleads are connected one each to the coil leads. The oddthing to me is they jumped a100Ohm resistor around each diode.The diodes would effectively block any feedback from one coil lead to the other but when you jump the resistors around the diodes itopens the circuit. What am I missing? What is the reason for the resistors? Here is a link.
http://www.amm.haan.de/Immognition/amm_qa.htm#revadapter