I have a 90 model F-150(in-line 6 cyl) that the windshield wipers only function in High(no Low or intermittent). I have changed the switch and the motor without correcting the problem. During my investigation, I found a black box attached to the lower dash support on the left-hand side(interior). It has a wiring harness which installs in series between the bulkhead disconnect and the wiper switch. What is this black box? What is it's function? Could it be the source of my windshield wiper failure?

Thank you, oldmopar

 

Could be. That box was called the Interval Delay, something like that. Not used in the later trucks, the delay was done differently.

 

If you turn the **** all the way to the left you have a stop, then turn to right about 1/4 turn and you'll feel a stop. That's off, then continue to right and feel two more stops (Low & Hi.)


When I first got my '87, the wipers didn't work....after tracing the whole system and finding that I was getting power to all lines I was supposed to (wiring diagram here helps), I pulled the motor apart. Turns out the magnets on the case pulled off and were stuck on the rotor windings.

Well, after wire brushing the inside of the case to near white metal (shiny) and cleaning the magnets with degreaser and brake cleaner, I epoxied them to the case with J.B. Weld. Still running after a year.

Get a Haynes manual and trace all the wires to their ends, checking for continuity and then voltage. CLEAN ALL CONTACTS with cleaner and reinstall and remove and reinstall a couple of time to get good contact. If this don't work see below.


Try and find an interval governor at junk yard. Next stop would be a dealer. The interval governor is solid state with a solenoid and at least 1 diode internal.

If your electronically inclined you could try and figure out the values for the diodes and resistors after testing them. then replace as necessary.

 

Thanks to Larry Derouin and the non-member who answered my message. The black box is called the inverval governor. I replaced mine with a new unit and all is well now. Internally, my failed unit had a rather large heat sink which came loose at the solder joints. I intend on repair this and keeping the old unit as a back-up.