This pull-up resistor is used to make our standard (non-ZST) 3-3/8-inch and 4-5/8-inch tachometers work with 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 factory computers will require this part to function correctly with a standard tachometer.