Thanks to Art Cutler for this diagram and explaination!!!
I finished refurbishing my 1968 Series 1.5 wiper motor. It now runs at low and high speed as well as returns to the park position when it’s switched off. That’s all the expertise I can claim regarding wiper motors. Here’s a schematic I drew by inspection and summary of what I think I learned – hope it’s of some use to others with this one-year-only wiper configuration.
- The motor assembly is based on a Lucas DL3A motor (mine has p/n 75658A dated 6/68). There are 3 leads coming out of the motor (green, red, brown) as well as a black motor case ground lead and a red wire extending from the motor to the parking switch. I believe this is the only year the parking switch is part of the motor assembly.
- Power (+12V) goes to the green lead. The dash rocker switch grounds the brown and red leads to run the wiper motor on low speed. The brown lead is held open (only red lead grounded) to run the wiper on high speed. The motor returns to the parking position when both the red and brown leads are opened – the motor grounds itself through the copper disk in the parking switch until the contact arm reached the gap in the copper disk.
- Motor speed is controlled by two field windings. The primary winding is copper colored wire with may loops. The secondary winding is white insulated wire with relatively few loops (see attached photo). Grounding both the red and brown motor leads results in current to only the coppered colored winding (both ends of white winding are grounded). Opening the brown lead activates the white colored winding which reinforces the field created by the copper winding.
- The white colored coil appears to add significant additional resistance to the copper/white coils now running in series resulting in a reduction in current passing through the coils and a net reduction in the overall field strength relative to the copper colored coil working by itself.
- The Lucas DL3A motor is a DC shunt type motor, i.e. armature and field wired in parallel. These type motors are constant speed motors which draw significantly more current when under load. Reducing the field strength causes an increase in motor speed – sounds odd but lots of technical websites support this.
- Oscillating motion of the wipers is produced by a motor drive pin rotating at a 1 5/8″ radius while driving center and right wiper pins with a 2″ radius as well as a left pin with a 2 1/4″ radius (LHD car). The resulting wiper sweep angles (assuming my 50 year-old trig still works) are 108 degrees for the center and right wiper arms and 92 degrees for the left wiper arm.
Hope this is useful – let me know what I got wrong!