Lighting is simple: Get a cheap multi-meter. Set to Resistance/Ohms and find ground by clipping to each wire, and touching bare (unpainted) metal somewhere - exposed bolt heads are usually good enough to find ground - Tip: Ground wire is almost always solid black, black with a different color stripe, or a different color with a black stripe. All other wiring will not have any black in them. Once you find ground, switch to volts (use DC setting) and move to the next wire. Have someone step on the brake and find the one that reads between 10-12vdc. Then have them turn the lights on, find the one that has 10-12vdc which will be your marker lights. Then to make it easy, turn on your emergency four-way flashers and find the one that will jump between 0 and 10-12vdc. Lastly, backup lamps - your buddy will need to put it in reverse - and you'll probably need to have the truck running - but it's an older model - so maybe you can just have them put it in run without actually starting it. I've attached the 2017 RAM 1500 wiring diagram. Shouldn't be much different even though you have a earlier generation.