hooking up spedo for th400
Go to the link above and follow that. Some incorrect info in the link--a sensor out of a 4L60E/700R4 will not work, they are 2" in diameter, a th400 is 1 7/8.
You could go to GM for the sensor and reluctor wheel. There are two reluctor wheels, one has a small ID for 27 spline outputs (1988-1990 2500 truck th400/3L80) or large ID wheel for 32 spline output shafts 1988-1990 3500 truck th400/3L80/3L80HD)
Your stock wire harness should plug right into the new sensor.




