If you are handy dandy with a volt meter I say go for it - if not find someone who is. First find out if you have the right voltage coming from the plug on truck without trailer hooked up (parking lights, turn signals, brake lights etc.) should be 12 to 14 volts. Make sure you have the right plug. With the trailer plug unhooked from truck - put 12v on each pin on trailer plug (don't forget the ground hook it to the trailer) see what comes on and then write it down. Make sure the pins coincide with pins on truck. Brake to brake - parking to parking etc. Sometimes people have problems with their wiring and instead of fixing they just put patches to make it work or move wires around.
Plug everything up and start working backwards from the lights. Make sure you have 12 v at light (if yes bad bulb or usually bad ground) (if no start tracing backwards towards the plug and see where you lose the 12v and that is likely the area of concern - a splice or joint of some sort. Lots of times you have bad grounds and you don't want to mess with those they will make you go crazy and very difficuly to diagnose
. Hit brake lights and turn signals come on - hit turn signal and parking lights go on - go figure - thats bad grounds for ya. Make sure you have good ground between trailer and truck. Sometimes a visual inspection of lights will tell you its a bad ground and sometimes a meter will say its good and visually it looks good but its not. All I can say is have fun - hopefully bad plug - sometimes its easier to just rewire the whole trailer....
John