wiper motor electrical... issues. =/ (1988 bronco 1)

[ShadetreeSeattle]

Having a tough time with this one, pretty decent at electrical troubleshooting, I have the ford FSM/EVTM for 1990 F series trucks. (mines an 88, but close enough) I have to be missing something here. Pinpoint tests told me to replace wiper motor, did that and it performs same as original motor, they do the same thing. replaced the dash switch, same thing. played with combinations of original switch and motor. it all does the same thing, consistently.
it's the two plug wire harness harness type motor, where it's got a connector for motor itself and a connector for, as far as I know the park switch on the motor basically. (it has the intermittent wipers module with the standard dash mounted turn CCW for intermittent wipe, turn CW for Low/High) not the column mounted switch, idk when they moved off to that setup. i think 94.

The problem:
something has gone wrong in which the switch body is going live 12v, which shorts out if mounted in dash. I accidentally found this out, playing with it while installing the new switch. it only however works at low speed, and only when switch in the high speed setting.

it also only will work with the intermittent module bypassed, directly connecting the switch to the wire harness connector. if the intermittent module is connected, it shorts out and i get wipers which work for like 20 seconds, at the same, low speed then the circuit breaker in the switch starts tripping, giving me. well... intermittent wipers, at the decision of the circuit breaker which really sucks if you live in washington lol.

Side note, i drove this rig all the way form san diego like this, it was not fun haha. if i jumper the blk/light green +12v to either the low or high speed circuits it works just fine. i literally ran two wires from the switch socket and jambed them into a crevice in the dash paneling. i pinched the wires toghter to intermittently operate, twisted them together to run at low speed.

it seems that the low and high speed work fine, but perhaps its something in the park circuit which is shorted? been pulling my hair out on this one. i don't think i metered enough stuff, it's likely something obvious. original wire harness seems unmodified, but that doesn't rule out much. i think after writing this that i need to go thru and check everything for shorts again, something is getting shorted when its suposed to be 12v. the weird part is that if directly jumpered at the switch harness, both low and high speeds work fine, no shorting, no overcurrent, barely even spark when i plug the wire in, as expected. ***? lol. halp. thanks all.

 

[ShadetreeSeattle]

made some progress, on the BLK/PNK wire its shorted to ground, with both the wiper's park switch disconnected and the interior switch and intermittent module. as i see in the diagrams, it shouldn't be grounded with both ends of the wire unplugged. so now, its play the game of... where's the short. its shorted pretty well, wherever its happening, wiggle test with a continuity tester doesn't change. prob going to just have to peel off the tape and loom and visually inspect the whole thing.

 

[Tiha]

Sounds like you have got it narrowed down in a hurry. Could be a couple wires melted together in the harness. Might find more than one.

Do you CA guys need wipers?

 

[johnnyreb]

Sounds like you have got it narrowed down in a hurry. Could be a couple wires melted together in the harness. Might find more than one.

Do you CA guys need wipers?

I heard it never rains in Southern California---IT POURS

made some progress, on the BLK/PNK wire its shorted to ground, with both the wiper's park switch disconnected and the interior switch and intermittent module. as i see in the diagrams, it shouldn't be grounded with both ends of the wire unplugged. so now, its play the game of... where's the short. its shorted pretty well, wherever its happening, wiggle test with a continuity tester doesn't change. prob going to just have to peel off the tape and loom and visually inspect the whole thing.

Have you checked for ground wire being bad? I,d goo with a ground wire and see what happens. Trying to find a short is tiresom. I,d also go to where the wiring harness . Passes throught the firewall. Especiall since it has some age on it. From the factory the spray a coating on the outside of the firewall on the wiring harness. To keep moisture out.,but in time that stuff gets hot and melts between harness connection. Their should be one bolt holding it together on the outside. Sometime they are a pain to get apart--because they are behind the master cylinder. Cleans both parts--the one inside the cab and the one under the hood. MAKE SURE YOU UN HOOK THE BATTERY----AND AFTER YOU CLEAN BOTH SIDES REALLY GOOD---LET BOTH SIDE DRY FOR ABOUT 12 HOURS OR LONGER---TO MAKE SURE THE CLEANER YOU USE IS COMPLETELY DRY. Then hook it up and try it. I have found it has solved some of my problems.

 

[ShadetreeSeattle]

took me long enough to reply! haha

it ended up being the intermittent wiper module/me believing that a more modern wiring harness could be backwards compatible with just plugging the switch plugged in, with the module removed.

i thought this because in my 77 f250 i was able to easily add an intermittent module i found at the junkyard, and the switch to upgrade to having intermittent wipers. but between 79-89 the wiring harness and motor was modified slightly and as a result you cant just temporarily delete the wiper module and plug the switch in because of a subtle wiring change concerning the park switch on the wiper motor.

the park/low speed circuit gets shorted on purpose to halt the motor from potentially rolling past the park switch and continuing another cycle, or just continuing to run. I'm sure we have incountered at some point in our lives when this circuit or the switch fails and the wipers never turn off.

anyways, the original module was failed and me believing that one could just plug the switch in directly to the harness made me believe that something else was awry, until i saw in the wiring diagram how the module itself prevents that short from happening. if the module fails it leaves the low speed grounded resulting in the motor only working on high setting and spinning at about 1/2 speed, until the autoresetting circuit breaker starts getting tripped, which gets you the jumpy, mostly useless wiper action. i thought it sort of poor design that if the module fails, it doesn't fail in a safe state, it was a lazy design choice because ford didn't want to update the entire wiper harness.

the way i got around this until i figured it out was to temporarily remove the switch and module which eliminates the wiper park circuit and jumpered the black green v+ and blue white high speed wires. a terrible idea because it eliminates the overcurrent protection, and the wire fell out a few times while driving in the rain (always while dark) haha but it worked.