Technically there isn't any switches in the wiper. Continuous 12 volt feeds all but a small spot in the magnetic field. The 12 volts off the dash switch fills in the dead spot which starts the wiper and parks in the same spot when the switch on the dash is turned off.
Years ago I went thru about six of the TNK wipers I have. One is missing the weight that restricts the motor enough to stop in the dead spot. One wiper was missing the weight and it would coast past the dead spot and keep running without power to the switch terminal. If it would have done the same mounted and wiper against the windshield I'm not sure. The post the weight is mounted on is between eleven o'clock and twelve o'clock in this picture.
View attachment 3843074
These.also came in a mirrored version. A 62 production had one of those as well as one in a group of three I brought off eBay years ago. Because of how much harder it is to return anything pre 3/69 when Toyota dropped everything earlier from their parts system I've never researched if these were have the wiper park on the outside of the windshield and come together when running or RHD and LHD versions.
This actually brings up a question about how that weight works.
I believe the motor design is what is called a two pole brushed
PM+++ DC motor. The wikipedia page illustrates is pretty well:
Brushed DC electric motor - Wikipedia - https://en.wikipedia.org/wiki/Brushed_DC_electric_motor
+++ Edit: I take that back. These motors are not PM motors I don't think, because there is a field coil wrapped around the steel core of the stator. This suggests that the magnetic field of the stator is induced when this coil is energized. The late 60s early 70s motors are PM for sure, which are mounted inside the cap.
From what I read, this dead spot in the magnetic field occurs when the poles of the armature are in line (and oppositely charged) with the poles of the stator magnets, like the image at the bottom here:
Tutorial: Brushed DC Motors (Part 1) - https://www.automate.org/motion-control/industry-insights/tutorial-brushed-dc-motors-part-1
Torque is zero at that position. During running, the rotational inertial of the rotor prevents stalling on this dead spot.
Now to my confusion:
There is actually a permanent magnet on the weight above, which you can see peaking out at 12 o'clock in the pic above. Is the purpose of this to advance the rotor just slightly when power is cut to prevent it from stopping in the dead zone? I noticed that the PM in the weight is repulsed from the rotor when power is applied, which suggests to me that it is mounted in a configuration such that the PM is magnetically the same pole as that side of the rotor when it is at that part of its travel (ie south pole to south pole or north to north).
Maybe we are getting into semantics here, but there is what I would call a park switch mounted under the contact terminals on the motor itself. Instead of grounding out the motor like the early 70s models when the plunger is raised, its job is to provide 12V to the S terminal just long enough to park the blades when the S terminal is switched off via the dash switch. I believe the + terminal sees +12V at all times, and the S terminal see +12V only when the dash switch is turned on. This is according to Coolerman's diagram.
When the park plunger raises the park switch connecting the + terminal to the S terminal, it breaks the connection. Current coming from the + wire is no longer supplied to the S terminal, thereby stopping the motor.
my fault about the screws. I will search the bench top and send them over. It’s a pain that you have to remove them to take the switch cover off.
