Lucas wiper motor wiring

How to wire an older Lucas wiper motor for two speeds with one relay.
I'm not sure if this will work for the newer motors. My wiper is from a 1961 Jaguar Mark IX.

Latest update:  5/8/2015
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Wiper schematic




Theory of operation:


The "Park" switch closes as soon as the motor starts running and opens on each sweep of the blades when they reach the parked position.

The park switch is bypassed by the wiper switch and the motor runs continuously when the  DPDT switch is placed in either the "fast" or "slow" speed.

The relay is wired to run the motor "slow" when not energized. The relay is energized only for "fast" speed. This is done so that when the wiper is switched OFF the parking switch will keep the motor running at a low speed until the park switch opens. If "fast" speed was used for parking  the motor will overrun the park position and keep running. Originally Lucas shorted the motor winding out to cause the blades to stop very quickly. I find that my wiring circuit does not cause overrun.

The wiper can be made to run intermittently by momentarily grounding the GRN wire. The motor draws a maximum of 3 Amps unloaded. I used a 7-1/2 Amp slow blow fuse.



Wiring the motor:

The motor wire colors are listed below. Wire colors outside the motor are the ones I happened to use. These are the electrical abreviations of the colors.

+ voltage from thermo switch .... GRN-BLU     (Positive voltage from thermo switch)
Top of field ................................ GRN-WHT    (Positive voltage to field winding)      
Field tap ..................................... GRN-BRN     (Slow connection)
Bottom of field .......................... GRN-YEL      (Fast connection)
Wire from thermo switch .......... GRN               (Positive voltage to the thermo protection switch)
Wire from motor "-" .................. GRN-RED     (Negative connection to armature)

          NOTES:
1. Electrically connect the Green-Blue and Green-White wires together. Insulate the connection.
2. Wire from Park switch to the motor is external to the motor case and is BLK.
3. Old Jaguars are wired with the positive terminal of the battery grounded. This accounts for the GRN wire now being the positive wire instead of a wire with RED in the color combination.



Component and construction tips:

The relay is a DPDT 12 volt automotive type relay with the contacts rated for at least 10 Amps.

A DPDT center OFF switch is used as the "High-OFF-Low" speed switch. Contacts must be rated for at least 10 Amps at 12 volts.

Be sure to wire the GRN-BRN wire to the normally CLOSED contacts of the relay. Use wires of AWG 20 or larger. This will insure that the voltage presented to the motor does not have excessive voltage drop.

One contact of the DPDT switch is not connected to anything. This is the run "slow" position of the switch.

The positive 12 volts from the battery is connected to the fuse and then to the center connection of the DPDT switch. The other center connection of the switch is connected to the battery ground. USE SLEEVING! You don't want these connections to short together.



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