Originally Posted by opietrials
I recently purchased the caps and lights for my 2011 WRX premium. In the process I also found out that the mirror harness is not available separately, you have to buy the mirror assembly which comes pre-wired with the correct harness. This leaves you three options: splice into the wires that you need and put small female spade terminals on the other end to plug into the lights, or buy the mirror assembly with the wiring already there, or try to add the pins needed to the current mirror harness plug and find the correct plug for the indicator light.
You're better off just adding the wires to the plug. I wish I did this route rather than buy whole mirrors - it would have saved some money and it's not that hard to do.