The wiring schematics for the DRL is in the US factory manual. This is because DRL is an option on US Rangers (fleet vehicles). up until 2005, they were a module behind the bumper, left side. It had cooling fins on it. If I recall correctly, it contains a relay and resistor to reduce the voltage output. Pre-2005 vehicles have a jumper wire to short the connection and allow the lights to work without the module...that's what most people have...just a plug with a loop wire on it. Every Ranger since 1993 has been pre-wired for the DRL...if you take out that plug and put in a module, you have DRL.
The module is a single unit and replacing it solves most DRL problems unless you've got a wiring or connection issues somewhere down the line.
Post-2005, I believe it's controlled by hooking the truck up to a Ford computer and navigating through the lighting menu where you can turn it on or off. It's in there along with the seat belt chime disable and a bunch of other stuff. Requires a Ford computer, but it should be in there. I've never seen it, just heard that.