The electrical lighting system of a towing vehicle typically includes brake and turn signal lights mounted on the rear of the vehicle for indicating vehicle braking or directional changes. Specifically, illuminated brake lights indicate a slowing or stopping vehicle, while illuminated and flashing turn signal lights indicate a turning vehicle. Typically in late model vehicles, the turn signal lights and brake lights are independently connected to the electrical lighting system of the towing vehicle and have separate filaments. The brake light filament is typically connected directly to the vehicle brake, while the turn signal light filament is typically connected directly to the turn signal indicator.
When the vehicle is used to tow a trailer, the lights on the vehicle are obscured, so it is necessary to include a separate set of brake and turn signal lights on the trailer. Each brake light and turn signal light on the trailer, however, is typically combined into a single light having a common filament. The single filament functions both as a turning indicator as well as a slowing or stopping indicator.
Consequently, in order for the trailer light to indicate the correct directional signal, it is necessary to adapt the independent turn signal and brake lights of the towing vehicle to the combined turn signal and brake lights of the trailer. Therefore, a trailer light adaptor circuit is typically inserted between the electrical lighting system of the towing vehicle and the electrical lighting system of the trailer to adapt the towing vehicle's lights to the trailer's lights. The adaptor circuit, for example, can be inserted between the trailer tap terminal on the towing vehicle and the wiring harness of the trailer, as shown in U.S. Pat. No. 4,842,524 issued to the assignee of the present invention.
Prior art devices have attempted to adapt the electrical lighting system of the towing vehicle to the trailer lights. For example, Bryant, U.S. Pat. No. 4,006,453 shows a device for adapting the independent brake and turn signal lights on a towing vehicle to the combined brake and turn signal lights on a trailer using two logic circuits, one circuit for each side. Bryant discloses logic circuits having npn transistors, silicon controlled rectifiers or relays connected between the electrical lighting system of the towing vehicle and the trailer lights.
Although Bryant discloses a circuit for adapting the electrical lighting system of a vehicle to the trailer lights, there remains a demand for new and improved electrical circuits which perform the same general function while providing manufacturing, operational and cost efficiencies. In this regard, late model vehicles typically have on-board computers and sophisticated electronics to control the engine function and the electrical lighting system in the towing vehicle. The prior art electrical circuits may in some instances permit some feedback from the electrical lighting system of the trailer to the electrical lighting system of the towing vehicle.