1989 ford f250 p/u. About a year ago windsheild wipers stopped working properly. Intermittent & slow speed do not work and fast speed works slower than normal but only back & forth 3-4 times before stopping altogether. Must turn switch off & back on brfore wipers work again. I've changed motor & switch twice each & voltage regulator with no improvement.
Check the ground going to the body from battery and engine to body also check switch to seeif proplerly grounded. Also check the threee things I have pointed out in diagrm. You may have a bad interval govenor.