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I have a '90 F250 that had a similar problem when I bought it. I already had a '91, which had that problem, which was caused by a loose ground pigtail on the wiper control module. A bump to the dash panel just above the brake release handle would remake the ground, and things were fine for a while.
So, I thought it was the same problem with the '90, and while checking the ground, I noticed some buzzing from the control module, so I took it out, but could see nothing obvious wrong with it, put it back and continued trouble shooting, finally deciding it was a bad wiper motor, which I remove.
I found the issue was in the switching mechanism in the motor, that mostly seems to be to control it going to park position. Replaced the wiper motor, everything is is fine.
I have a '90 F250 that had a similar problem when I bought it. I already had a '91, which had that problem, which was caused by a loose ground pigtail on the wiper control module. A bump to the dash panel just above the brake release handle would remake the ground, and things were fine for a while.
So, I thought it was the same problem with the '90, and while checking the ground, I noticed some buzzing from the control module, so I took it out, but could see nothing obvious wrong with it, put it back and continued trouble shooting, finally deciding it was a bad wiper motor, which I remove.
I found the issue was in the switching mechanism in the motor, that mostly seems to be to control it going to park position. Replaced the wiper motor, everything is is fine.
Hope this info is helpful to you.
Soooooo. Replace the wiper motor. That's easy enough.
I have a '90 F250 that had a similar problem when I bought it. I already had a '91, which had that problem, which was caused by a loose ground pigtail on the wiper control module. A bump to the dash panel just above the brake release handle would remake the ground, and things were fine for a while.
On my 88 I had a similar problem. I had a bad ground on the wiper motor. It was a short black wire if I remember right. I think it may attach to one of the mounting bolts. You may try that first, if not that I think it is the wiper motor.
Depending on which motor you have, you could pop off the park switch cover and clean and relube the contacts inside. I did that on my truck years ago for the same thing occurring. It's worth a try before pulling the wiper motor out to replace it.
It's not fun getting the bolt off the drive post to wiper link when stuck, I had too take off the cowl and unbolted the wiper pivots to get better access to it when I replaced one before for loose magnets.
the wiper delay module is a printed circuit board. over time the board breaks. the fix is buy a new module for around $100, or take it apart and resolder the board.
you can look for one in a junk yard, but they are getting pretty rare as these trucks are now 30 years old.
The delay module is a black (?) box about 3" cube. If I remember correctly is is close to the parking brake. Very close to the harness for the wiper switch. They said when the parking brake is released it it rattles the module. Then over time it breaks the solder connections. I resolderd mine and it did not work, I opened it up again and resolderd all the connections and now it works great. So if you open it up go over them all. I think mine did not work on intermittent and low. High speed it was fine.
Mine were doing the same. Because of a loose switch, I replaced both the intermittent style switch (the one with the black pigtail) and the motor. It's a time consuming job to replace the motor, that is made more interesting on a slightly lifted 250...you really have to stretch and balance on a short step ladder to reach it without laying on to of the engine...at least my 5'11" self did.
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