How do you keep the stock cluster and tach working behind an LS/4L60E without cutting the factory harness?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

• LS Control System kit: The Chevrolet Performance LS Control System includes a tachometer signal in the bulkhead connector. (Chevrolet Performance)
• LS Control System kit: The white bulkhead wire is the tachometer signal with a 2 pulse-per-revolution output. (Chevrolet Performance)
• LS Control System kit: The tach signal is a low-voltage square wave, and some tachometers or transmission controllers may need a pull-up resistor to read it. (Chevrolet Performance)
• Gen IV 58x (19201327 kit): The 19201327 kit's white wire is the tachometer signal with a 2 pulse/rev output. (Chevrolet Performance)
• The SGI-8 is a signal interface unit for converting tachometer signals. (Dakota Digital)
• The SGI-8 can recalibrate an ignition system tachometer signal. (Dakota Digital)
• The SGI-8's signal input accepts the ignition system tach signal from the negative side of the coil or a tach output. (Dakota Digital)
• The SGI-8's OUT3 output equals OUT1 divided by 2. (Dakota Digital)
• The SGI-100BT is designed to recalibrate a speedometer and/or tachometer signal. (Dakota Digital)

Confirm against the instructions for your exact parts before wiring. More: Tach and speedometer signals in our tuning guide.