Turn off the circuit breaker to the switch controlling the Elco 4-inch low-voltage light fixture.
Measure the distance between the joists, using a tape measure. Adjust both of the Elco 4-inch low-voltage light fixture's hanger bars' lengths to match the distance between the joists, using the tape measure as a guide. The small end of each telescopic hanging bar slides in and out of the hanging bar's large end.
Hold the bottom of the Elco 4-inch light fixture's hanger bars even with the bottom of the joists. Run a 1-inch wood screw through each of the hanging bar's screw holes, using a Phillips screwdriver to tighten the wood screws.
Remove the screw holding the Elco light fixture's junction box cover in place, using the Phillips screwdriver. The junction box mounts to the light fixture between the bulb housing and the transformer. Set the junction box cover aside.
Insert the end of a slotted screwdriver into the slot in one of the knockout covers, located on the side of the junction box. Move the knockout cover back and forth until it breaks free. Discard the knockout cover.
Insert a wire clamp's threaded end into the junction box's knockout hole. Reach into the junction box and tighten the wire clamp's nut.
Push the wire set from the switch into the wire clamp on the Elco light fixture's junction box.
Twist the black wire in the switch's wire set and the black wire in the Elco light fixture's junction box together. Cover the wire ends with a wire nut.
Spin the white wire in the switch's wire set against the white wire in the Elco light fixture's junction box. Lock the wires together with a wire nut.
Combine the copper wire in the switch's wire set with the green wire in the Elco light fixture's junction box. Screw a wire nut over the wire ends.
Replace the Elco 4-inch low-voltage light fixture's junction box cover. Tighten the cover's screw.