Ford Mustang Forum - View Single Post - GT middle two (fog?) lights. Keeping them on!
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post #9 of (permalink) Old 01-27-2011
wingless
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Joined: Aug 2010
Location: Boca Raton
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Yes the wiring may be modified to permit the fogs to be on with low beams and high beams.

The logic for this control is within the Smart Junction Block. The fog lamp relay is integrated into this assembly.

The feed to the fog lamps is a brown / yellow wire connected to pin 3 of the Smart Junction Block.

The fog light indicator lamp is fed by a brown / yellow wire connected to pin 6 of the Smart Junction Block. This wire is +12V when the fog lamps are illuminated and 0V when off.

The fog light switch is a grey / violet wire connected to pin 49 of the Smart Junction Block. The fog lamp switch drives this to ground, presumably to turn on the fog lamps.

There are lots of ways to modify the vehicle for this change. The simplest-to-understand way to implement this change is to add two additional 12V SPDT relays.


The relays have a coil side and a SPDT switch side.
  1. Connect one end of the coil on each relay together.
  2. Connect the switch common on each relay together.
  3. Connect the normally open switch contact on each relay together.
  4. Cut the fog light switch grey / violet pin 49 wire from the Smart Junction Block and connect the wire to the two common coils connected in step 1. (The wire end, not the Smart Junction Block end.)
  5. Connect the other end of the coil to +12V that is hot when the vehicle is running.
  6. Cut the fog lamp feed wire, the brown / yellow wire connected to pin 3 of the Smart Junction Block.
  7. Cut the fog light indicator lamp wire, a brown / yellow wire connected to pin 6 of the Smart Junction Block.
  8. Connect the feed wire (step 6) and the indicator wire (step 7) together.
  9. Connect the feed / indicator wires connected together in step 8 to the relay switch commons connected in step 2 together.
  10. Connect the open end of one coil to the left low beam feed, the brown / blue wire at pin 13 of the Smart Junction Block. Do NOT cut the pin 13 wire.
  11. Connect the open end of the other coil to the high beam feed, the yellow / violet wire at pin 2 of the Smart Junction Block. Do NOT cut the pin 2 wire.
  12. Connect the relays normally open contact that was connected together in step 3 to the fused side of F21, the 15A fog lamp relay.
These changes will permit the fog lamps to be on when the vehicle is running and be on with either the low beams or the high beams.

With any wire project, always disconnect and secure the battery negative terminal.

This is an involved project and should only be attemped by those with expert wiring experience.

2011 GT Mustang - Performance White / Brick Red - Cashmere : 401A : Brembo : Electronics PKG : Spoiler Delete : 3.73:1 : Glass Roof : Comfort PKG : Security PKG : HID
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