Abstract: A control device for a first lighting load on a vehicle or trailer features an input connected to a lighting circuit through which a different second lighting load is operated, thus placing the controller in parallel relation with the lighting circuit, and a power output connected to the first lighting load on the vehicle or trailer. The controller is configured to detect from the input, a signal change sequence in the lighting circuit that comprises an initial high-to-low signal downstep, and a subsequent low-to-high signal upstep completed within a limited time window triggered by the initial high-to-low signal downstep. In response to detection of this signal change sequence, the controller energizes the first lighting load. If the second lighting load is the vehicle headlights, for example, a user can turn on the first lighting load by momentarily flipping the headlight switch off, and then quickly back on again.