Crossover Confusion

A very difficult concept to grasp in wiring is how to connect multiple 5-wire power window switches to just one window such as having a switch on the driver’s door to control the passenger window in addition to the passenger door switch. If you don’t do it right, and many don't, you are guaranteed getting a direct short to ground when you try to activate the second switch.

Let’s back up and review a bit.

The majority of power window motors, and I believe ALL aftermarket units, require reverse polarity to operate. This means that  they do not case ground, they have two wires and those wires must be provided both positive (+12v) and negative (-12v) to work, that is (+) to one wire and (-) to the other. To reverse the direction of operation, the polarity must be reversed to both wires. So we’re not just turning a hot (+) feed on and off, but rather switching which wire gets (+) and which wire gets (-). That makes things more complicated.

The internal design of a 5-wire switch takes care of that polarity reversing but in doing so the design also has BOTH output terminals connected to ground when the switch is in the neutral or “off” position. These switches actually have 2 ground wire connections coming into the switch - one connects to one output and the second to the other output. When you push the switch, it disconnects one of the outputs from ground and switches it to positive, leaving the other output grounded, thus providing the +/- or -/+ to roll the window up or down. This grounding in the neutral position is where the problem comes in when you want to add the second switch. If you connect the second switch directly to the motor leads and apply a hot (+) signal, the juice back flows through the crossover wiring to the ground connection of the first switch and ZAP, you blow the fuse. If the first switch is activated, the juice grounds through the second switch with the same result. What to do?

The solution is to not wire both switches directly to the motor leads but to put the leads from the first switch through the second switch. The OUTPUT wires of the first switch become the crossover wires feeding to the second switch. For the second switch, the inputs normally connected to ground ARE NOT. They, instead are connected to the crossover wires from the first switch so that the second switch is actually “grounding” through the first switch by means of the crossover wiring. 

When the first switch is activated, one of the crossover wires flips from ground to hot, the juice passes right through the connections of the second switch and on to the motor. Since the second lead is still grounded, the motor sees the correct (+) and (-) and runs. On the other hand, if the second switch is activated, it disconnects the ground signal from the first switch for just one connection and replaces it with a positive feed while the second connection remains grounded and, again, the motor runs, all without a short circuit. Should both switches get activated at the same time, they will either both be sending the same signal to the motor and it works, or they will each be sending a (+) signal to one of the motor leads. If the motor sees a (+) on both leads simultaneously, it does nothing - no current flows, no short circuit, no problem.

Still confused? No problem! Remember that we are here to make sure you get the parts you need for the job that you are doing. We’ll get you set up right and show you how to do it.

Watson's StreetWorks      http://www.watsons-streetworks.com