There is many thread about tachometer in this forum

I have fitted Autogauge Electrica tachometer (suitable 1-10 cylinder).

This tachometer was sensitive about interference. I must put 10k ohm serial resistor to sensor line. Tachometer has been in use two years and it has worked well.

Suitable tachometer types depends your bike model:
Models 2004 - 06 are twin spark => spark plug fires once per crank revolution.
My bike is 2007 and it is single spark type => fires once per two crank revolutions => tachometer must support single cylinder mode.
I don't know about 2008-12 models

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MODs - XTX/XTR wheels - Supermoto front fender - Handguards - Engine crash bars - OTR Bash Plate - Renthal 971 Handle bar - Bi-Xenon lights - Auxiliary Driving Light LED - LED tail light mod - Speedo healer - GiPro gear indicator - Thermometer - Heated Grips - Navigator - Tachometer - 12V Output plug - Front Spacers 30mm + 15W Fork oil - Lowered seat 25mm - Adjustable side stand - Kev Fuel Mod - DNA Stage 1&2