I am trying to find out if it is possible to disconnect the turn signal function from the brake light, my problem is that here in Finland turn signals must be orange and under no circumstances flash red, so I have made a separate back up light and I have put orange bulbs in original back up sockets now I need to make original brake light to work as parking/driving light and brake light, ther is now a third funktion it also flashes when I put turn signal on.
I have noticed that there is one green wire with a red stripe that brings + to the bulb on both braking and turning, is it possible to somwhere disconnect that turn light function?
It's all done in the steering column. I do not know what year truck you have, but on the later ones Ford calls the turnsignal switch the "multi-function switch" because it also has the high/low beam and the hazard flashers(maybe the wipers also).
Most all American cars and trucks are setup the way you are describing, and the turnsignals and the brake light wiring get mixed together and co-ordinated in the turnsignal switch. It will be easier for you to take the original wire in the rear that did the turn and brake(one different wire for each side), and move it down to your new orange bulb. You will then have to go up and find the wire that goes from the brake pedal switch to the turnsignal switch, cut it so it no longer feeds the turnsignal switch(this is usually a lightgreen wire most years) and then splice it to a new wire that you add in, run this new single wire all the way to the rear along the frame rail, and then tie it into the original red light sockets. Tie it into the driver's side and then splice and run it over to the pass side also. This will be your new red brake wire.
The original red bulb should also still have a brown wire going to it, this is the marker/running light wire and you still need this. The brown wire feeds both taillights in the rear and the license plate lights.