custom taillights

most custom taillights are 2 wire hook up. my truck is a 3 wire, the turnsignal is separate. i have a trailer module on it right now, but when i hit the brakes the turn signals blink really fast, like the bulb is out. its annoying. anyone know of another way to hook up 2 wire taillights to a 3 wire system? or is it maybe i have a cheap module? thanks