I replaced my trailer tail lights
with LED bulbs last year, which were direct replacements for the existing #1157 socket. Before the replacement, my trailer lights worked fine driving in the daytime, but at night with the van lights on they would sometimes light
improperly when the brakes
and/or turn signals were applied as well as everything else, especially if interior appliances were also using power at the same time.
A typical incandescent tail/brake/turn light bulb uses a substantial amount of 12 volt current, about 3 - 4 amps each. A typical automobile alternator has a current output anywhere from 30 (very old) to 50-70 amps, and vehicles are generally designed to use about 80% of the alternator capacity while driving. This means that you likely have only 10 - 15 amps of current as "spare capacity" in a tow vehicle, less if you installed a bigger stereo, the fan is going full blast, and the kids run a laptop while driving.
That is why your headlights may dim a bit while you are idling at a stop light at night in the pouring rain with the wipers and fan going. The current demand from the car at that moment has exceeded your alternator and is drawing from the battery
So having the extra 6 lights for the trailer can mean a noticeable increase in overall load current, which it did on my vehicle, and it can bring you close/over the limit of the alternator at times. Since replacing the two trailer tail lights with LEDs (which use only about 5% of the power of incandescents for similar brightness), I have not had this problem and the lights work properly all the time, even at night when the stereo is going full blast and the kids have computers plugged into the car. I still left the side running lights on the trailer as incandescents, since I didn't need to replace them to solve the problem.
I note that LEDs actually emit only a very narrow spectrum of light, so you should get red LED bulbs for red tail lights, orange LED bulbs for orange side lightinig, etc. Because of the narrow spectrum, a white LED bulb behind a red tail light lens will give you very little or no light at all. It is not like an incandescent bulb, which gives off light of all frequencies and so can be filtered to any colour.
Also, as pointed out in an earlier post, the size of the trailer wiring is important, as is having connections in good condition. It is worth replacing much of the trailer running light wiring with bigger wires, if convenient. It is especially worth making sure that the connection between the tow vehicle and the trailer wiring is in good shape.
Hope that helps.