03 accord dual climate 70 7864dz

Hi everyone, I am using the 99-7864 to replace my factory radio on my 03 accord with the dual climate control. My question is when it comes to getting the rear defogger to work. When you use the 7864 on the models which do not have the electronic climate controls, all you have to do is just plug the factory hvac harness into the 7864 and the defogger and everything works. Its just plug and play. I unfortunately have the electronic climate controls so I had to purchase the 70-7864DZ adapter as well. The instructions say to run the wire that comes with that adapter through the firewall to the engine compartment, go to a plug under the underhood fusebox, take apart the plug and then put their wire in, all this to get the rear defroster to work. This doesnt sound right to me and I was wondering if any of you experienced guys could tell me if their is another way and how you did it. Thanks

Anybody have any thoughts on this. Thanks in advance.