Testing tach

[spareparts]

thats how i do it, I have a spare tach with leads wired to it, it has aligator clips on the other end, I check for voltage(purple wire) first, then check ground(black wire) if they are good to go, I wire up my spare tach, hook up the grey wire(signal) and see if my tach works. Its best to unhook the old tach first, in case its shorted to ground