The VR1.5 will take power from the positive 12v (blue wire) and the negative (black w/ white stripe wire) from your decoder and output a steady, highly accurate 1.5 volts on the tan wire. This is ideal for working with 1.5v bulbs in situations where resistors are unwanted or unusable. Designed specifically for use with the T4X and T6X, the VR1.5 can be used with any decoder where the the ground and common are available for wire attachment. Dimensions: .7” x .425” x .16” or 17.78mm x 10.795mm x 4.064mm