Hi, all.
Does anyone know what voltage the tachometer on a Kymco Yager GT 200i works at? I know it taps off the "downstream" side of the ignition primary coil, the wire that goes to the ECU that dumps voltage through the coil to ground to induce the high secondary coil voltage... so is it just measuring how many times per minute the 12 volts drops to zero, since the "upstream" side of the ignition primary coil is +12 V?
Or is the tachometer relying upon the secondary coil inducing a higher voltage in the primary coil as it discharges across the spark plug, and reading that (the back-EMF off the primary coil can reach as high as 300 volts).
The reason I ask is because I'll be replacing the OEM ignition coil with a Pertronix FlameThrower HV 60,000 volt 1.5 Ohm coil. It'll have a higher back-EMF voltage than the OEM coil, so to protect the ECU and tachometer I'm going to put an "ignitor" downstream of the ECU that'll act as the switch for the primary coil, and as isolation protection for the ECU and tach. But I still want the tachometer to operate, so the ignitor will have a tach connection on the protected side.
But in order to do that, I need to know what voltage the tach normally uses as its signal. If no one already has the info, I'll break out the digital voltmeter and tap into the yellow/black line on pin 12 of the ECU.
