No matter which manufacturer produced your pop-up camper, and no matter what form of drive actuates the roof movement, a system of cables and pulleys, springs and a winch will raise and lower the roof. You may winch the roof up yourself, use an adapted power drill, actuate a pumped hydraulic system or use an on-board battery to power an automatic winch, but the stranded cables will still be in part of your camper. They transfer the force of the winching mechanism to the lifting mechanism so are under considerable stress both when deploying and retracting the extending section. They are the only part of the mechanism ever likely to fail.
Extend the pop-up camper roof. If the broken cable prevents you from doing this normally, lift the roof with automotive jacks and brace it with poles held firmly in place by clamps.
Strip away the panelling or shrouds that disguise the horizontal cable runs up each corner. You will see a pulley in each corner inside or immediately beneath the floor. Spray a silicone lubricant onto the crank, the cables and all the pulleys, then wait 15 minutes.
Locate the distribution block that manages the movement of the cables to raise and lower the roof; its position under the camper varies by manufacturer, so check with your operator's manual. From this distribution block the cables run through a system of pulleys to the camper's four corners, where they are routed into the telescoping supports. Follow all the cables from the distribution block to their ends, inspecting them until you find the broken one.
Use a socket or wrench to release the nut holding the pulley which routes the broken cable, then feed both halves of the cable out through its conduits or guide tunnels. Release both ends with a screwdriver or wrench depending on your manufacturer's system; most cables are trapped between two plates which are clamped together with a nut/bolt/washer assembly until the cable cannot slip.
Obtain a replacement cable that exactly matches the size and weight of the broken one. A reputable recreational vehicle dealership should be able to arrange delivery in one or two days.
Fit the new cable in a reversal of the extraction procedure, consulting your owner's manual to determine whether the manufacturer suggests feeding it in from the roof or distribution block end. Ensure the entire cable is precisely seated in its pulleys and guides. Reassemble the shrouds or panelling.
At the end of every camping season inspect your cables for signs of fraying and replace any worn ones before using the pop-up camper again. Depending upon your manufacturer the distribution block will be actuated by a threaded rod or a chain. It is important to follow the manufacturer's instructions for greasing these components at the start of every camping season.
Several pop-up camper manufacturers recommend silicone spray to lubricate the pulleys and pushrods. Silicone spray will attack canvas. Always shield the fabric of your pop-up top with a large cardboard shield when using silicone spray. Broken cables are not repairable. The strain they are under when in operation can cause them to separate with considerable force.