Wiper switches & governors.
To convert a pre-'92 truck from standard to interval wipers, unplug the dash harness from the standard switch (E7TZ-17A553-B), remove the switch & discard it, connect the dash harness to the black side of the interval governor (E1UZ-17C476-A), connect the red side to the interval switch (E7TZ-17A553-A), and ground the switch's wire to the dash structure, cowl, or ground wire in the harness. With the key in run, all wiper functions should work normally. If so, install the switch, and place the governor in the dash out of the way.
To bypass a pre-'92 truck's interval wipers, unplug the dash harness from the interval governor and plug it into a standard switch. With the key in run, all wiper functions should work normally.
For '92-96, see these captions:
YC2Z-17C476-A WCM
