What wire circuit powers the backup lamps?

Circuit 140 BK/PK (black/pink), which carries 12V when the vehicle is in reverse.

What relay controls the trailer backup lamps?

The Trailer Backup Lamps Relay in the Trailer Relay Box; it directs current to operate the trailer backup lamps and outputs 12V on circuit 963 R/Y when energized.

Which connectors serve the left and right backup lamps?

On Chassis Cab: C447 (left) and C448 (right). On all other configurations: C433 (left) and C434 (right).

Where do the backup lamp circuits ground?

The lamp grounds join at splice S404 and go to ground G100 (see Grounds page 10-4); the trailer relay grounds via circuit 57 BK through splice S102 to G100 (see Grounds page 10-1).

What circuit feeds the trailer backup lamps from the relay?

Circuit 963 R/Y (red/yellow), routed through connectors C149, C424, and C417 to the trailer backup lamps.

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Ford Bronco/F-Series Backup Lamps Wiring Diagram 93-4 - Trailer Relay & C433/C434

Ford 93-4 Backup Lamps wiring diagram with chassis cab backup lamps and trailer relay box circuits

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Wiring diagram for backup lamps showing left and right backup lamp circuits and trailer backup lamps relay with color-coded wires.

AI caption July 2018 · Photo 335 of 386

This document is page 93-4, "Backup Lamps," a factory-style wiring diagram covering the backup (reverse) lamp circuit. Power arrives on circuit 140 BK/PK, energized at 12V in reverse. A branch labeled BRONCO feeds the Trailer Relay Box (referencing Power Distribution page 13-2), where circuit 37 Y (12V) and circuit 140 BK/PK operate the Trailer Backup Lamps Relay, which "directs current to operate trailer backup lamps." When energized, the relay outputs 12V on circuit 963 R/Y through connectors C149, C424, and C417 to the trailer backup lamps; the relay grounds through circuit 57 BK via splice S102 to ground G100 (see Grounds page 10-1). The vehicle backup lamps split into two configurations: Chassis Cab uses splice S426 feeding connectors C447 (left backup lamp) and C448 (right backup lamp) on circuit 140 BK/PK; All Others uses splice S426 feeding connectors C433 (left) and C434 (right), with lamp grounds joining at splice S404 to ground G100 (see Grounds page 10-4). A reader can learn wire circuit numbers, colors, connector identifiers, splice points, ground locations, and how trailer backup lamps are relayed on Bronco applications.

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Frequently asked questions

What wire circuit powers the backup lamps?: Circuit 140 BK/PK (black/pink), which carries 12V when the vehicle is in reverse.
What relay controls the trailer backup lamps?: The Trailer Backup Lamps Relay in the Trailer Relay Box; it directs current to operate the trailer backup lamps and outputs 12V on circuit 963 R/Y when energized.
Which connectors serve the left and right backup lamps?: On Chassis Cab: C447 (left) and C448 (right). On all other configurations: C433 (left) and C434 (right).
Where do the backup lamp circuits ground?: The lamp grounds join at splice S404 and go to ground G100 (see Grounds page 10-4); the trailer relay grounds via circuit 57 BK through splice S102 to G100 (see Grounds page 10-1).
What circuit feeds the trailer backup lamps from the relay?: Circuit 963 R/Y (red/yellow), routed through connectors C149, C424, and C417 to the trailer backup lamps.