Hey, I have a quick question about the external ignition coils and what the differences are between them. I was in a junkyard and spotted a Acura Vigor (not sure what year) and I opened the hood and come to find out it had a Tec TC-18a Coil on it (30520-PT3-A02). My 97 LX has a TC-19a (30520-PT9-A02) on it and My sisters 96 V6 has a TC-21a (30520-P0G-A02). They all look identical but what are the main differences in them? I also opened the hood of a 98 Accord V6 in the junkyard as well and it had a (30520-P8A-A01) which looked totally different.