This is a post about one of my customers. He has a 1964 Imperial (beautiful car) and recently had to replace the power window motor in the driver’s door. It’s a problem I’ve run into before, but always have to go to the drawing board to solve. Hopefully this helps anyone who is facing a similar problem.
His problem was, the old motor had two connections for power and was internally grounded. Depending on which connection received power, the motor ran clockwise (CW) or counter-clockwise (CCW). The new motor requires both power and ground to run. In order to switch between CW and CCW, you have to switch the power and ground wires.
Modern DC motors, that require both power and ground, use a Double Pole Double Throw (DPDT) switch with a center “off” position. The old DC motor only required a Single Pole Double Throw (SPDT) switch.
Some guys just hide a second set of DPDT switches under the front seat and leave the old switches unplugged. Naturally, this being a classic car, he wanted to keep both the look and the function of the old switches.
So, this is how you make a SPDT toggle act like a DPDT toggle and control a DC motor in both directions.
You’ll need two 5 Pin Relays to make this work.
[A normal, 4 pin relay is either off or on. A 5 pin relay is either A or B.]
Wire one relay to each of the motor contacts so that by default they are sending “Ground” to the motor.
Then wire the relays to the SPDT toggle so that when one of the switches receives power it sends “power” to the motor while the other switch is still sending “ground”.
Here’s the wiring diagram.
Here are the relays all wired up.
Here are the relays wired into the car.
What’s great about this solution is, you can keep the original SPDT toggles and make use of modern DC motors. Since the relays are wired to the motor, and don’t change the wiring to the rest of the car, this will work the same on the passenger’s door and allow both switches to operate the window with no extra work.