In-dash or Undercar.
Q: What is the difference?
A: Before discussing the difference let's explain the need for the harness. With any 1984-93 700R4 automatic transmission, a fluid activated switch controls the torque converter lockup. This was designed to increase the car's fuel mileage, but during in-town driving at lower RPMs the switch will cause the converter to lock and unlock. This will give the driver a feeling of "up and down shifting". The In-dash installs under the passenger dash in minutes. The Undercar unit plugs directly into the existing harness on the transmission. Complete instructions included Both will allow the driver to control the converter lockup by using a small toggle switch, which can be conveniently mounted inside the center console. For example, "on" for in-town driving or racing, "off" for normal highway speeds to regain peak fuel economy. Legal in California for racing applications only.