Disable daytime running lights on a Ford truck by disconnecting the resistor. Alternatively, enable the daytime running lights on a Ford by either installing a wiring harness kit from Ford or by purchasing a relay block and resistor and plugging them in.
Enabling the running lights system on a Ford is more difficult than disabling it. Sites like Ford150.net have diagrams to help you locate the resistor and relay block or where these parts go. In most cases, the parts are only available from aftermarket sources. Ford also sells a DRL kit that can be added to the wiring harness, which is typically located beneath a removable panel on the dash.
On Ford models from 1999 and after, daytime running uses the low-beam headlights at about 80 percent of system voltage. This happens through a DRL resistor interacting with low-beam filaments. When the headlights are switched on, the daytime running lights are disabled and the filaments get 100 percent of the system voltage.
For models previous to 1999, the daytime running lights system uses the high beams at a reduced voltage. The system is triggered when the ignition switch turns on, the headlights are off and the parking brake is released.