I just finished rewiring the power windows on my dads 81 GMC truck (455 Olds powered of course!). It suffered from the typical slooow moving windows. GM G body cars use the same wiring, and suffer from the same issue. All that is required to fix it are 4 single pole, double throw relays (commonly used in just about any GM vehicle) make sure it’s a black relay, and has 5 pins. Make sure you get as much wire from the donor vehicles as possible. Mount the relays somewhere in the door, as close to the motor as possible. ,
Use the above diagram to wire your relays. Use the heavy gauge pink wire to power both relays using pins 87. Don’t cut the pink wire to the switches, splice in additional wire going to the relays. You still need power on the pink wire to the switches. You will have to add your own ground wires on pins 87a and 86. Use 12-14 gauge wire on the 87a, 18 gauge wire will be plenty on pins 86. Refer to the factory service manual wiring diagram. Cut the dark blue and brown wires at each window motor, cut the wires just long enough to reach the relays connect the to pins 30. Connect the cut ends from switch to the dark blue and brown wires to pins 85 of each relay.
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