1987 Ford F150 2 wheel drive engine 300 straight 6 cylinder the windshield wiper only work on high speed they do not work on intermittent and low speed I have replace the windshield wiper switch to no avail
It sounds like the Interval Electronic timer in the wiper circuit is malfunctioning. According to the schematic the low and intermittent wipers go through the Interval Timer. There is a Service Bulletin on the replacement of this I'll try to list this below.
The interval timer is probably inside the wiper motor.
WINDSHIELD WIPER - INTERVAL - GOVERNOR REPLACEMENT PROCEDURE - SHOP MANUAL REVISION
Article No. 88-22-7
LIGHT TRUCK: 1988-89 F-SERIES, BRONCO
ISSUE: The interval windshield wiper governor replacement procedure as published in the 1987 and 1988 Light Truck Shop Manual, Volume A, Section 35-60-14 has been revised. This revision only applies to Bronco and F Series vehicles because the governor mounting bracket retaining screws are hard to get at.
ACTION: If service is required, use the following interval windshield wiper governor service procedure. This information should be inserted into your 1987 and 1988 Light Truck Shop Manual, Volume A, Section 35-60-14 for future reference.
1. Disconnect the electrical connectors from the governor.
NOTE: DO NOT REMOVE THE OLD GOVERNOR FROM THE VEHICLE.
2. Connect the electrical connectors to the new governor.
3. Position the new governor on the 14401 wire harness above the fuse box.
4. Make sure the new governor is not contacting any other components and tape it into place with black electrical tape.