Oh so let me tell you about my fucking car repair yesterday
So, my front windshield washer hasn't worked for a while, and I needed to fix it before I go on a 1400 mile road trip on Wednesday. I knew the fundamental failure points already - motor, relay, fuse, okay
It's a Car Part, they mostly work the same. Pressing the button on the wiper stalk produced no howl from underhood so, okay, the motor isn't running. So I check for a fuse.
The manual lists no position for a washer fuse. Wipers sure but no washer, and the wipers work. This is irritating but, whatever. I do some googling - I mean, there literally has to be a fuse, even if it's shared with something else. Everything in cars is fused.
Some forum threads say fuse 13. One says fuse 19. The manual disagrees and says those are unused spots - curiously they have fuses in them but, okay. The fuses are also fine. Later I find another thread that says #30 underhood; it's also fine.
I go looking for a relay. This also produces no results, and now I know some bullshit is up. There's no possibility the pump operates without a relay, modern cars don't work like that. So I know I'm being fucked with, but I don't yet know the shape of the simulacrum.
I look for a schematic. Also no dice. Infuriating, but okay. I buy a replacement pump - this is all in the parking lot of the parts store - because that's the hardest thing to get and drive home to seethe at it.
I get under the car to remove the pump. The car's a 2003 so the fluid hoses are stuck on real real good and i can't figure out where the fasteners are. After some frustration I realize the pump is just held in by friction, and I pry it out.
I had a bucket fortunately because the gallon of washer fluid of course drained right out. Oh and it drained onto the inside of the bumper making it impossible to avoid making a huge mess and my beach towel got soaked in Fluid.
Plug in the new pump and hit the button and no joy. I'm not surprised at all by this, I had nearly zero confidence this would fix the problem. Mostly this is because things pretty much don't just break anymore. I never thought this was a real equipment failure.
At this point I'm confident that the problem is not in the meat of the system, but one of those modern car problems - a computer is confused and sourly refusing to turn on my washer pump, is my theory. I dig for documentation for a while longer
I found what looked like a magnetic reed switch in the bottom of the reservoir, certainly a float sensor. I test it with a meter and a very small PAX fridge magnet and it works perfectly. Analysis says the go condition must be open circuit and it's open, so it isn't the problem.
More googling, more googling. Finally I find a forum thread that seems to address the problem but makes no sense, it's talking gibberish. I stare at it for a while
Finally I conclude that the thread, which reads like a fever dream, must be the answer because nothing else makes sense. The thread asserts that there is a washer relay in "the front wiper assembly" which is nonsense, but whatever
I pry off the front wiper cowling, and wouldn't you know it, there's a huge fucking cable harness going into the WIPER MOTOR. These mother fuckers put the washer relay AND A MICROCONTROLLER inside THE CHASSIS OF THE WIPER MOTOR.
I would find you a picture of this huge multipin plug by the way, but my car, despite being a fantastically popular and heavily maintained model, is non-existent if you want electrical information. You can find 02 and 06, but not mine.
At this point the forum thread is no longer helping me, but thank fucking God I remembered the Chilton's I bought when I got the car and stuck in a seat back. I dug it out and lord Almighty it had a schematic.
The schematic was infuriating of course because, hooray, microcontroller. There's just this huge block in the diagram that's a Mario question block and who knows what's inside. 
This is not the exact schematic btw, it's just very similar. Like I said, my cars electrical system is not available online.
After staring at it and swearing about forty times I start to make sense of it. Sort of. See, here's the pump, and we can follow the wires up and down
This means the wire coming out of the wiper motor that powers the pump is black with a white stripe. I find that wire but I can't test it from the wiper motor end because everything is heavily weather sealed.
The forum threa was from someone whose black/white lead had broken, so I had to assume there could be some kind of design flaw. There was no way to get an ohmmeter between both ends to check it though.
The only way to resolve this was: I stuffed a tiny Allen wrench in the multipin plug, alligator clipped it to 8' of speaker wire, crawled underneath, stuffed a resistor lead in the pump connector and measured resistance. Continuity, so, fuck.
Schematic shows the wire exiting the wiper stalk button. It's violet on mine. I check it and I get 12v when I press it.
So like... it has to be the relay at this point. But I turn on the key, hit the button and this time, listening closely, now that I know where it is I can hear the relay clearly in the wiper motor. So what the fuck?
The motor has 12v, the relay is switching, continuity is good, what in the fuck could be wrong at that point?
So I turn my attention to a part of the schematic that had been bugging me.
So I turn my attention to a part of the schematic that had been bugging me.
The north end of the pump in the schematic goes to the relay in the wiper motor. But on MY version of this schematic, the south end of the pump goes to... "REAR WIPER RELAY". huh? what? why? what? huh?
It takes me a while to figure this out, but it did dawn on me, and I was furious at Ford, and furious at schematics with no english explanations in them.
So here is the beginning of the great reveal on this prestige TV episode.
The car has front and rear windshield washers, but only one pump. How the fuck does that work? I assumed there was a solenoid, but honestly, that's not very "car", the auto industry doesn't really work that way.
This is the pump. I was upset at it from the get go because I didn't get what was going on. Two outputs - presumably one to front, one to rear, but how would it choose? Solenoids, no. That doesn't read. Driving a positive displacement pump into a closed line? Nah. Nah.
After staring at it for A LONG GOD DAMN TIME it dawns on me. The motor is goddamn REVERSIBLE, and the impeller drives fluid out of only ONE OUTPUT depending on the DIRECTION OF ROTATION.
Clockwise for front washer, counterclockwise for rear. THAT is how the auto industry works, so I accepted this the moment I thought of it. Of course. Of course.
Now, reversing a DC motor is "easy". It looks like this - a double pole, double throw switch can do it. But notice, it's *two* switches. This was the hint I needed.
In order to reverse the direction of a motor, you need three switch positions: Forward, off, and reverse. Relays don't have 'off' positions, so you need two to achieve this. You could use a DPDT to pick direction and a second one to turn power on and off, orrrr
You can do what Ford did, which is to use a pair of double pole *single* throw relays. Both ends of the pump are grounded by the relaxed state of each relay, and when you press one button or the other it puts +12 on one side or the other.
Now, is there a *sensible* reason for the rear relay to literally be in the BACK OF THE CAR, despite being controlled by and controlling a motor that is all the way in the front? Fuck no! But you can sure bet that's what Ford did!!!!!
This is an EGREGIOUS breach of abstraction but go off I guess
The rear wiper motor is fucking unplugged because it's in a dump. I backed the car into a tree and shattered the rear window, and when I got a new one from the junkyard for $70 I found out Ford changed EVERYTHING except the hinge and latch mounts.
So my half-liftgate has no hydraulic lifts, no defroster and no wiper because Ford decided to Iterate and make the parts completely incompatible. THE FRONT WINDSHIELD WASHER WOULDN'T WORK BECAUSE THE REAR WIPER WAS UNPLUGGED. VERY NORMAL ENGINEERING.
That's it, that's the story. I put an alligator clip on two pins of the rear wiper connector and it's fine now. Fuck Ford, fuck auto engineering, fuck this shit.
By the way, after this I was already absolutely seething and *completely* exhausted from getting under the car and back out a dozen times and running into and out of the house a dozen times and I still had to do an oil change on a hot engine.
It was like getting kicked in the balls for the *second* time
OH, one more thing: I do not excuse Ford putting a microcontroller in the way of the washer control one bit. There is ZERO logic to the washer circuit - the fluid level sensor isn't even part of it, I've run that pump dry before. It's literally BUTTON > RELAY > PUMP.
I have no idea why they had to shove a fucking microcontroller in there but the auto industry managed to scoop the entire tech / iot industry by 15 years in terms of putting computers in places they have no right to be, doing a worse job than a single 15 cent semiconductor.
