Well, first, you didn't specify the vehicle. Secondly, I don't think you quite grasp how transmissions work. The shift cable would be what makes a transmission go into reverse, and that'll be operated either by a manual lever (the shift column) or by an electric solenoid (in push-button transmissions).
It is important to know the location of the different car parts. The Reverse Gear Light Switch is located on top of the gearbox in most cars.
on the gear box look for wires going to switch
gear box
on the transmssion, no matter which of the 3 (3sp,4ps, 5sp) its really a reverse switch, see? reverse gear engaged switch.
model t ford
on gear box to side near filler plug or on top of gear box
on the side of the gear box
This question omits important required information: Make Model and Year of car Type of gear box.
probably located on top of the gear box
probably located on top of the gear box
There is a switch for the reverse sensing system located on the dash just to the right of the instrument panel dimmer control. When the ignition is on and the gear selector is in reverse, this switch can be used to disable or enable the RSS . If the system has been disabled the off indicator remains illuminated, so press the switch again when the ignition is on, and the gear selector is in reverse to return the system to the ON position.
Immediately passed the Park position. Neutral separates the Reverse gear and the Drive gears.