Those add-ons can get ya sometimes. Trailer plugs are another prob area.
That's what terminal blocks, auxilliary fuse-blocks, solder, and heat-shrink are for.
Everything I have wired/added myself is in far superior condition than the cheapy "harness" that Ford put in.
Where the problem begins is when people splice into the already over-taxed/under-wired factory system, and especially when they do so in a shoddy manner such as scotch-locks, suit-case splicers, cheapie crimpers, big wads of black tape, etc.
That is one of the many reasons why I keep preaching that the trailer plug should always be independent of the factory wiring and the factory headlight switch should in no way affect the trailer markers---not even via a relay, the trailer markers should be controlled by a switch entirely their own; the same goes for any added truck markers, running-board lights, tailgate lights, etc.
