Best Way to Test Vehicle Wiring to Find Wire for a Specific Lighting Function

Question:

What colors on the Ford 2003 F 150 Wiring harness are for on the tail lights. I cannot find a schematic on them.

asked by: Bill

Expert Reply:

Auto makers do not always consistently use the same wire color for any given lighting function. If a vehicle production line runs out of a specific wire color they will switch to another wire color. This is rarely if ever documented.

For this reason it is always best to test the wiring with a circuit tester like # PTW2992 to determine which light function on the vehicle appears on any given wire. Please refer to the linked video. The other way to find out the running light circuit's wire color is to remove a tail light assembly and trace the wire leading to the tail/running light bulbs.

On the trailer side of things tail/running lights most often are carried on a brown wire, such as on the 4-pole connector # W787264.

expert reply by: Adam R