I have had great results with wired and wireless speedometers, I do mount my ignition coil behind engine as far away from speedo as possible and I have found that using a suppressor/ graphite core sparkplug wire really helps block what I believe is called RF interference, I cant tell any performance difference between a solid core wire and the suppressor core wire on my bikes, but it will allow the wireless and wired speedos to work without acting crazy.
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