The SN10K is a pull-up resistor to make our standard (non-ZST) 3 3/8” and 4 5/8” tachometers work with GM LS-series engine.; LS engines put out a weak four-cylinder tachometer signal and this part installs to boost the signal to the tachometer to one it can recognize.; Most stock ECM GM computers will require this part to function correctly with a standard tachometer.