I was able to reach the connector without any disassembly, though it took about 15 minutes of concerted looking to find it in the first place. It was taped to another bundle, so I had to cut the electrical tape to free it up enough to get the necessary angle to reach it with the horn plug. Using a pair of long needle nose pliers, I was able to hold it while pressing the horn plug in.
Using this plug is really the best way to go for heated grips because it's relatively easy and the circuit is keyed, so if you forget to turn off your heated grips, they won't drain the battery. I think heated grips are wonderful. I've only recently installed mine and already used them twice. It's summertime in Vegas and believe it or not, I'm not carrying heated gloves (because I don't own a pair, but not likely to be carrying them around in the summer time if I did). So I ride up to the mountains, from 2,400 ft to 8,400 ft elevation and guess what - it's cold! Heated grips save the day because they're right there when you need them. I'm not saying they would keep your hands warmer than heated gloves, but they keep your hands a darned sight warmer than no heated gloves, no matter the season.
'04 DL650 - Blue, 57,000 miles, well personalized, gone but loved
'08 WR250R - Goes anywhere
2012 Yamaha Super Ténéré - makes the DL redundant