I've gottem many A1, A2, and a few A3's through GL. None have ever had the 12 pin plug removed. Some have been damaged beyond use, but never removed.
It is very easy to adapt the existing wiring to civi vehicles though. Get yourself 4' of 4 strand trailer wire (heavier 7 strand actually works and looks better, but you only need 4 wires: ground, tail lights, and right and left blinker), what ever plug your towvehicle requires (I always use the large round 7-blade RV plugs), 1 pr of 1156 and 1pr 89 automotive bulbs (those are the ones I've used every time). Replace the 24 volt bulbs with the 12 volt bulbs in the light housings (on some trailers the top screw can be hard to get at and every once in a while a screw breaks off, it's not a big deal) but leave the lense covers off till you're done (makes it easier to see whats going on getting the wires hooked up right). Assemble the 4' piece of trailer wire and the plug end you've chosen so it can be plugged into the tow vehicle. On the trailer frame is a tin guard covering a connecting block, remove the cover to access the block (usually a philips screw or 1/4 " socket). Don't just pull them all out of thier holders. It may be much easier if you know where they are at to start with. The rest is really just trial and error for getting the wires hooked up right. Hook up to the tow vehicle and use the light and blinkers to determine the correct connections. The ground is easy, hook it up first. The other three wires you need (if still in the holders) are usually but not always the three toward the rear of the trailer. At this point it really helps to have a helper to watch the lights. If everything is correct, the 89 bulbs should be your tail lights and the larger 1156's should be your blinker and brake lights (brakes opperate through the blinker wires when completed).
If you would like I can get some pic of one of mine I've switched over tommorrow morning. Let me know if I can help.
Good luck.
This whole process takes me about 15-20 mins now, My first one took about 2 hrs.