What Have I Done Wrong

[Bry]

I noticed the reversing light wasn't working on my 2001 fiesta flight today but all the bulb is fine so i checked the fuse box not sure which one was the right one, all fuses fine. I then unplugged/ plugged the light cluster connector and even checked the auxiliary fuse box under the bonnet removing one fuse I thought was the right one. Now not only is the reversing light not working but the car won't turn over I suspect the immobiliser is engaged. What do I do to disengage the immobiliser. From a light out to a non starter, any ideas anybody, have I done something stupid..