On my Silverado, I decided not to cut into the wiring with diodes as I had done on previous trucks. One of the reasons for this....if your vehicle taillights (dual filament brake and turn signal bulb) come on when the towed is turned off and you step on the brakes, you'll have an issue when turning and braking. When you come to a stop, with your turn signal on, the brake light will override the turn signal when using diodes.
On my Silverado, I went to AutoZone and bought the new flat taillight sockets and bulbs. They are smaller and are easier to fit into the lens. I used a dremel to cut the rectangular opening.
This system makes life easy....no cutting into wires, no drain on the towed battery, no magnetic lights to put on and take off (get stolen) and fool proof operation.