ok - so, after putting in my wipers I have a bug to fix - the wiper park feature doesn't allow them to return - so I'll address how I fixed that.
When turning off the wipers in any position, the wipers should return back to the "off" position no matter where they were when turned off. And they don't.
I got the wiper motor off the bracket (this had been recently "rebuilt" so it was disappointing that it wasn't all tested, but there you go…
Undo the two long bolts on the top of the black housing that houses the magnets and remove the housing - the armature will come with it and the brushes will pop out and flap around on the brush plate - not a bad idea to remove the springs behind the bushes and put those aside - this looks a bit daunting but it's not a problem really.
Remove the 2 screws that hold on the tin cover and you can see the worm drive on the end of the armature, it drives the white plastic/nylon gear which has a small reduction gear on the back, which turns the large gear on the output shaft. Grab some pliers, pull out the metal spring-clip that loads the end of the armature, remove the circlip (not shown) from the top of the nylon gear. It will likely have a couple of shims between the clip and the gear - keep these.
Pull out the white gear and you can see at the bottom of the shaft the end of the cam follower and the cam/driveshaft thrust plate (probably not the correct name).
Ensure the nut and lever is removed from the bottom of the driveshaft - push up from the thread and once the drive shaft is out, remove the cam and thrust plate.
You can see the cam on the back of the drive shaft - this is spun by the reduction gear from the back of the white nylon gear, which is spun by the armature when voltage is applied via the brush plate.
The voltage is applied to the low or high speed wires & brushes until turned off when voltage is then applied to the red wire which SHOULD make the motor return to the park position.
Undo the 3 brass screws and remove the brush plate. When at the park position, the cam pushes the follower up which pushes up on a long black plastic rod into the underside of the brush plate.
Remove the black plastic rod
This is the PARK switch (I've never seen this in any picture so hopefully this is useful for you) and it operates in two positions: When the dash switch is turned off, the wipers are likely to be in mid-sweep and the motor is spinning. When the dash switch is turned off, 12V is applied to the red wire which allows the motor to keep turning until the cam lifts the black pole, which lifts the "tongue" and breaks the contact. The contact that allows the motor to keep turning is UNDER the "tongue" which when raised by the black rod moves the tongue from the red wire 12V to ground via the contact on the top (the underneath contact is where the red tube is pointing) the ground contact is the one most visible in this pic: When the motor is spinning and no voltage is applied, it becomes a generator, so grounding this wire forces the armature to STOP in the right position - if your wipers keep going when the dash switch is off, it's probably because these ground contacts aren't being made (and they need cleaning as per the instruction below) so the armature is just spinning past the cam location (and re-applies 12v to the armature and off it goes again....)
When the Park function works, the 12v contact sparks each time the contact is broken and eventually oxide builds up on the park switch contacts under the tongue and eventually stops it making a reliable connection. Fold some fine wet/dry sandpaper and force it between the contacts underneath and sand the contacts back and forth to clean them to restore operation to your Park function.
So - reassembly: Re-install the black post, put in the driveshaft thrust plate and the cam follower. Put in the driveshaft (this will likely push out the O-ring at the outer end of the housing, so watch for that - spinning the shaft often as it goes in often allows the O-ring to stay in place - but it can be pushed back in with a screwdriver once the driveshaft is in place. Put the washer under the lever at the end of the drive shaft covering the O-ring and then install the lever and tighten the nut - getting this all back into the bracket can be a pain but it will fit if you remove the nut again when fitting it up. Alignment here is important - when the cam operates the park switch, the lever should roughly line up with the armature/magnet housing, not be pointing out the top. Replace the metal clip for the top of the armature and install the white nylon reduction gear.
Install the brush plate and the three screws, make sure you put the ground brush wire back in under the screw. Then get a fine screwdriver and force up the tabs at the outer ends of the brass holders that house the brushes. Support the holders as you do this, they aren't the strongest items in the world...
Once all three tabs are folded up, put the brushes back in and make a little room in the middle for the armature's commutator - don't put the spring back in first, leave them out.
Make sure the brushes are pointed the right way to meet flat against the commutator and then put the armature back into the gearbox body:
Put the springs back into the brush holders from the outside and then fold down the outer tabs to hold them in place - don't let the armature fall out or you'll have to put it back making sure the brushes are all lined up then do the folding bit again - they'll only survive limited folds so be careful.
Slip on the outer magnet housing again - the magnets will pull on the armature as it goes on so jam a screwdriver into the worm gear so it can't come out (or you'll be back to do the brushes part again) - it can be a little tricky to get the top end of the armature to go into the bush in the housing, so wiggle it around and you'll be fine. Put in the two long bolts (mine would only go back one way - they didn't appear to be the same, but yours may differ) and once that's all buttoned up then install the gearbox cover with the two screws, not forgetting the ground wire goes on one of them.
Pack it with grease and you should now be good to go - rest it on the export brace and wire it up and test it.
It will make a racket vibrating on the export brace, but ignore that. If it's all good, then re-install it hook it up and connect the wipers. Don't push the rubber grommet back through the firewall until this final test - run the wipers, make sure they start and stop and park as expected. If the gearbox operation is too noisy or vibrates, then there is likely to be too much play between the lever (on the end of the driveshaft) and the gearbox housing - shim that up a little with thicker/more washers or a spring washer (mine was missing) and minimise any play, and it should quieten right down.
Hey presto - all fixed.
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