Hi Rob
This was specified for a Cobra 5370, but it worked on my 6422, it may by worth a try. (My radio keyfob is cobra head with two grey buttons and does not have an led, I just held it on for ~15sec.)
Auto learning procedure for radio keys:
1. With the system disarmed switch 'ON' the ignition.
2. Insert a touch key into the touch key recepticle, the dash status L.E.D. will permanently illuminate.
3. Press both radio key buttons, together, until the radio key L.E.D. stops flashing and goes out (about ten seconds)
4. Release the buttons and the radio key L.E.D. comes 'ON'
5. Press one radio key button, the radio key L.E.D. blinks and the dashboard L.E.D. goes 'OUT' for one second.
6. Repeat steps 3 to 5 for all other legitimate radio keys. When all keys have been taught switch off the ignition. (The dashboard L.E.D. will go 'OUT').
I hope that this helps.
Malcolm, November 2007