MG Car Repair: mga wiper motor, permanent magnet motor, wiper motors

Question
Hi, I have replaced the brushes in my MGA wiper motor (DR2?) but on reassembly, I do not have the wheelbox attached but it will not run. When I have connected 12V to the terminals 1 & 2 with no response. What should I look at next?

Answer
Hi Mark,

I have had many of those wiper motors apart because back in the days of the MGA we did not always have a new motor in stock to replace one with so we use to take them apart to try to repair them. As I remember on the two speed motors there were three wires going into the motor itself and it had a cancel switch (park switch)operated by a cam on the large gear. On the one speed motors they only had two wires going into the motor. The motor was a permanent magnet motor which meant you could reverse the direction of rotation by switching the two motor leads.

To test the motor it was just a simple matter of touching a power and a ground to each of the two leads to see if the motor runs and check the operation of the park switch.

On the three wire motors you had to ground one of the leads and quickly just touch each of the other two leads with a power supply. I don't remember the color codes of the three wires but even back then I remember all you had to do was to alternate each of the three wires as a ground to find the correct combination to see that both speeds worked. Then check the park switch to see that it was making and breaking contact as the large gear rotated.

Howard