Took the Defender out for a nice Sunday offroad drive a few weeks ago and after about an hour of driving the vehicle lost all power and died. Had to get it towed home. Marker Lights, Hazard lights, dash lights seem to work, headlight won't come on but I can flash the highbeams(No signal lights). It seems anything that requires the key "on" to work will not work. When I turn the key nothing happens(no fuel pump, nothing) I replaced the ignition switch nothing has changed. I have checked all the fuses I can find and they are all good, also checked all the grounds I can find everything seems to be fine. Could it be a relay somewhere? Any advise before I have to call in a mechanic? Thanks

 

It does seem to be electrical related, ground or relay. Could be the fuel pump relay if you are not hearing it pump when you turn the ignition on. Could also be the inertia switch.
Search over on Defendersource.com Lots of knowledgable NAS folks over there.
Best of luck.

 

Don't throw any more parts at it until you do a scan and see what codes it throws off - but double check the terminals are tight on the battery for a quick and easy that can do this