So he is talking about the small support trailers the drag week cars tow from track to track. A fused power feed directly from the battery. Then a relay for tail lights, two for brake lights/directionals. Tap into the rear tail light wiring harness to get each “signal” voltage for each relay. Only a small voltage will go through the car wiring. Tap into the driver side brake light wire and send it to drivers brake light relay. This relay output goes to the driver side trailer lights. Do the same thing for the separate passenger side brake lights relay. Then tap into one tail light wire on the car and run it to the tail light relay. The output from the tail light relay will spit and go to BOTH trailer lights. Drivers and passengers sides. Three relays and three splices into the car tail light harness.