[BraddahLikeScrap]

My bro just installed some LED bulbs on his brake lights, reverse lights, and side markers. When he pushes the brakes, the side markers light up along with the brakes. Note that there were no wire modifications, just simple screw-in LEDs. Anyone know what could cause something like this? I'll put up a video when i get the time.

[epoxi]

LEDs only need a tiny current to work, so maybe the wiring 'leaks' a little current to the side marker that usually isn't enough to illuminate the incandescent bulb. Try putting a resistor in series with the side marker lamps and see how it plays out.