Camper brake lights pick up power through the electrical connector from a tow vehicle. The connector is tied in to the wiring harness from the tow vehicle's lights. These connectors may sometimes come loose or have a bad connection, which causes an open circuit.
The power goes from the electrical connector straight to the tail lights and marker lights on the camper. Each of the lights on the camper is grounded close to the light on a good ground location. If a marker light or taillight is situated where there is no immediate ground, there will be a wire from the light to a remote location to be used as a ground. On some campers, all the marker lights may be tied in and grounded in a series. In this case, the camper shell is made of a composite that does not conduct electricity well. The lights have a wire running from one light's ground to the next and so on, and the final light will have the wire running from it down to the chassis.
This works OK, except when the ground gets corroded or loose, causing all the lights to go out at the same time. The same thing applies if the lights are wired in series where a singular power wire goes to the positive terminal of one light and then extends from the negative terminal of the same light to the positive terminal of the next light. Most all camper lights are parallel, where one main wire runs the length of the camper and all the lights have a separate wire attached to the main wire and they all have separate ground connections.
To start checking the lights, make sure the tow vehicle lights work to start with. With the vehicle lights on, check the camper electrical connector on the tow vehicle side for voltage with a circuit tester. Plug the connectors together and check the camper side of the connector for power. If it does not have power, the connector is bad.
Before replacing the connector, check for corrosion or pushed-out pins, then correct and test again. If there is no power, test the connection on the tow vehicle's wiring harness, where the pigtail is connected to the vehicle's wires. Make sure there is power on both sides of the connection. Repair as necessary. If the camper side of the connector had power but the lights did not work, check for a bad ground. Simply take a jumper cable with alligator clips and attach it to the metal frame of the light. Attach the other end to a good ground. If it comes on, repair the ground. If not, check the bulb and, if it is bad, replace it. If the bulb is good, check the center terminals in the socket and see if there is power. If not, check the other side of the socket where the power is going into the socket. If there is power, then the socket is bad. If there is no power, check the wire from the camper connector to the socket for a break in the wiring that prevents power from going from one end to the other. If there is, trace the wiring to find the bad spot and replace.
