clifford 50.7x wiring, 99 chevy 3500

Okay I am wrapping this alarm install up and have one last item to connect and that is the defogger output and I was hoping someone could give me a little help.  I am attaching a schematic of my wiring layout.  Does anyone have an idea on the best way to wire this up?  It would be great to be able to wire this into the existing wiring without adding a relay but I don't think that is going to be the case.  And, if I do need to add a relay how should I wire it up.

Thanks

I used a 30amp relay and connected as you would converting a negative input into a positive output.  I tapped the 12vdc constant going to the heating/ac controls with a 25amp inline fuse then to the relay and connected the output to the defogger wire.  It works the way it should but the inline fuse and the relay heat up.  The fuse heats up more than the relay.  I am not comfortable with that so I was hoping someone might have an idea on a way to install without the wires getting hot.  Should I remove the inline fuse between the power source and the relay and just use heavier wire and a 40amp relay?  The defogger is a 30amp circuit using 14awg for power and the output wire looks slightly bigger.  There is a ignition on power wire running to the heating/ac controls as well that is a smaller wire which I assume carries less current.  What about using that for my power source rather than the constant on wire since the defogger will only be used when the vehicle is running.  Also something that I thought is a little strange is when I activate the remote defogger the dash lights flash 2 or 3 times...is it suppose to do that?  It works fine except for the getting hot problem.

Thank you for any suggetions and help.