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Hello,

After reading multiple discussions on retrofitting a BMW E21 wiper motor to an Alfa 1750 (Australian delivered 1969), I cannot get it to self park. The BMW wiper motor has red, green, blue and white wires and the Alfa wiring inside the car blue, blue/black and white/black before it connects to a plug which then changes to green, white & red.

I have earthed the body of the BMW wiper motor to the body of the car, connected the blue Alfa wire (inside the car) to the green BMW motor wire which is working on lhigh speed via my high speed toggle switch (which is correct) and connected the white/black Alfa wire (inside the car) to the red BMW motor wire which is working on low speed via my toggle switch on low speed (which is correct). The only outstanding issue is that I have a wire from my fuse box which has permanent power on it which is not connected to anything (blue/black wire). Apparently on the Alfa motors, this was used to self park the wiper motor, however I cannot seem to get this to work on the BMW motor. I therfore have nothing connected to the blue and white wires on the BMW wiper motor.

However, if I connect the blue/black wire inside the Alfa to the blue wire on the BMW motor - nothing happens. When I connect it to the white wire, it blows a fuse. Any ideas? I am having trouble uploading the original BMW wiring diagram to this message however if you send me a private response, i can email it to you. All I know is that on 'windshield wiper motor schematic' 53a is blue (permanent run from fuse), 31b is white (park), 53 is green (slow) and 53b is red (fast).

Help as this is driving me crazy & consuming way too much of my restoration time !!!

AC
 

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Had the same problem and managed to solve it (albeit probably not very elegantly)
I have no electrical knowledge to speak of so my solution is bordering on a caveman level.

History of the E21
From what I've gleaned from the www, the E21 motor has an earth braking system (probably not the correct name!). Essentially the park function rotates the motor until it nears the 'park' position where a gap in the internal slip ring breaks the current. Inertia carries the motor on and normally it would pass the gap, in he slip ring, remake contact and continue rotating. While rotating without current the motor is now acting as a generator and earthing one of the brushes will create a large counter rotational force. This will bring the motor to an nearly instantaneous stop (ie at the desired park position).

In the BMW, the earth break system feeds through a control unit which must isolate any +12V feeds as the live park feed (as you've found out) will short out each revolution as the earth contact is made.

Our Alfas don't have electronics so the earth brake system can't be used (as far as Ive worked out) so I disconnected it simply by pulling the small contact tab off the base plate and insulating it with shrink tube.

Alfa red to E21 Blue
White E21 spliced to the White Alfa (or Green E21)
White Alfa to Green E21 (slow)
Green Alfa to Red E21 (fast)

note that if the E21 White is spliced to the E21 Red (fast) the higher momentum causes the motor to coast past the park point and it just keeps rotating
The park works on slow speed as the motor doesn't have enough momentum to coast pass the park gap especially with with the load of the wiper mechanism
This all worked except for the fact that the fast wouldn't go fast anymore. This was caused by the park feed through the blue E21 energizing the Slow speed brush (called field ???? something or other) which countered the fast speed..

So I installed an SPDT relay to isolate the park feed when the fast speed was in operation.

As I say inelegant and cavemanish but it works.

Attached are my sketches.

Note the removal of the back plate will be required if you've burnt out the contacts by earthing them too many times or for too long. (check for continuity after a couple of quick bursts on slow) Sand the slip ring and the contacts and then bend them back to shape.
You could remove the earth contact at this point but I've left it in in case someone else can give me a better solution using the earth brake.
 

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