I no longer own an Explorer/Ranger, but I'll chime in.
I have a backrack on my '06 GMC Sierra and forever wanted to mount another pair of taillights on it. When I have my kayaks in the bed it makes my stock taillights/turnsignals a lot more difficult to see during the daytime so this seemed like a practical/cool looking solution.
I found a great deal on ebay. Two lamps (with something like 62 LEDs in each), 2 grommets, 2 pigtails, and two mounting brackets for $35 plus shipping. I tried finding the same deal just now for this thread but no luck unfortunately.
Anyway, I had them wired just to come on with running lights and brake lights because my stock taillights had a separate wire for turnsignals... up until just recently, when I completely redid the wiring and instead tapped into the harness for my trailer hitch. It's very handy to have a test light because there's going to be a turnsignal/brake wire for each side of the vehicle.
I didn't have to use a resistor because my truck already has the supplementary LED turnsignals in my side-view mirrors. It's been wired up like this nice and tightly for about a month now, and before that, about a year. No problems with rapid flash or anything like that.
Granted, it is a little different than your desired application, but here's a picture:
Good luck!