problem with indicators

Hi, hopefully someone can help me out with a weird problem. Recently upgraded from stock mirrors to DP combined indicator/mirrors. At rest they work fine. At speed, however, the right side indicators don't work. Maybe 1/20th of the time. I've checked and rechecked the wiring (which was plug and play) and can't seem to find the cause of the fault. I figure if its a wiring issue it would either work or wouldn't, regardless of speed/load, so I am thinking I may have got a bad indicator? Any help would be greatly appreciated. Thanks