What triggers the relays in this auto headlight setup?

A White/Pink wire from the AutoLamp Mirror feeds the Parking Light Relay and Headlight Relay.

Which wire feeds the headlights from the switch?

Circuit 15 (R/Y), which goes to the MFS and to the headlights; the added relay wiring also ties into a Blue/Orange wire on the MFS.

How are the parking lamps connected in this modification?

The Parking Light Relay output connects to a splice on circuit 14 (BR), the exterior lamps wire, labeled 'To 14 (BR) Splice / Parking Lamps'.

Which wires on the headlight switch are always hot?

Circuit 38 (BK/O), which is always hot and connects to the fuse box, and circuit 195 (T/W), labeled Always Hot.

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Ford Bronco Auto Headlights Wiring Diagram - AutoLamp Mirror & Relay Add-On

Headlight and parking-lamp wiring diagram with relays and color-coded wires

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Wiring diagram showing headlight and parking-lamp relays, a multi-pin connector and color-coded circuits feeding courtesy, dome and exterior lamps.

AI caption January 2013 · Photo 547 of 3001

This is a hand-drawn wiring diagram, uploaded to a 1994 Ford Bronco gallery, showing how to add automatic headlights using an AutoLamp (auto-dimming/autolamp) mirror and two relays. The diagram centers on the factory headlight switch connector with its standard Ford circuit numbers and wire colors: 137 (Y/BK) Hot in ACC or RUN, 484 (O/BK) to the radio harness, 38 (BK/O) always hot from the fuse box, 195 (T/W) always hot, 14 (BR) exterior lamps, 54 (LG/Y) courtesy lamps, 55 (BK/PK) to dome lamps, 294 (W/LB) to the cluster dimmer circuit, and 15 (R/Y) to the multifunction switch (MFS) and headlights. Red lines show the added wiring: a White/Pink wire from the AutoLamp mirror drives a Parking Light Relay and a Headlight Relay, which tie into the 14 (BR) splice for parking lamps, the always-hot 195 (T/W) feed, the 15 (R/Y) headlight feed, and the Blue/Orange wire on the MFS. A reader can learn the headlight switch pinout/wire colors and how to interconnect the mirror and relays to trigger parking lamps and headlights automatically.

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Frequently asked questions

What wire colors and circuit numbers are on the Ford Bronco headlight switch in this diagram?: 137 (Y/BK) hot in ACC or RUN, 484 (O/BK) to radio harness, 38 (BK/O) always hot from fuse box, 195 (T/W) always hot, 14 (BR) exterior lamps, 54 (LG/Y) courtesy lamps, 55 (BK/PK) to dome lamps, 294 (W/LB) to cluster dimmer circuit, and 15 (R/Y) to the MFS and headlights.
What triggers the relays in this auto headlight setup?: A White/Pink wire from the AutoLamp Mirror feeds the Parking Light Relay and Headlight Relay.
Which wire feeds the headlights from the switch?: Circuit 15 (R/Y), which goes to the MFS and to the headlights; the added relay wiring also ties into a Blue/Orange wire on the MFS.
How are the parking lamps connected in this modification?: The Parking Light Relay output connects to a splice on circuit 14 (BR), the exterior lamps wire, labeled 'To 14 (BR) Splice / Parking Lamps'.
Which wires on the headlight switch are always hot?: Circuit 38 (BK/O), which is always hot and connects to the fuse box, and circuit 195 (T/W), labeled Always Hot.