Rob Barendregt has written a cool gauge that operates the afterburner from a switch in the cockpit rather than the Shift/F4 default method. The advantage is that it also switches in the afterburner effect operated by the aircraft smoke system as well as activating the reheat, whereas Shift/F4 doesn't do that. The gauge will only activate somewhere over 90% N1. It's on Avsim, search under Barendregt.