Recently changed from receiver pull to a 5th wheel travel trailer. I have always had a dead zone where they just did NOT seem to see my signals.
I Do not know for sure what I am going to do for box (tonneau--or toolbox). I bought a used tool box-- painted it flat black and added the side signals. YES; I KNOW NEW PICKUPS HAVE THEM!-- Mine has less than 30 grand-- will outlive me!--- also 30+GRAND cheaper than a new one. --
What I did was make an extension cord for my 4 flat trailer plug with an added female end by the male plug. I ran it under the box and up the right side front stake pocket put a female end on it there-- nicely tucked into the side of the box. I then wired the blinkers in the tool box to a trailer male plug--flat 4.
I tied back the wire for the stop/taillights, but left it there. If iI decide to add the red ones it will be extremely easy. If I decide to remove the toolbox for any reason; I just unplug it and remove the 4 --J bolts.
Just seemed a lot smarter than a lot of cutting and soldering under the truck. I DID solder and shrink or tape and the seal all conections! The wiring was also tied with zip ties in several places to keep from gathering mud! I do not go off main roads much, but, know what loose floppy wiring can cause! I used to have to fix it for ranchers that leased in the national grasslands.
No crimp connections--GUARANTEE of trouble here! Especially during the monsoon season!