Main thing for electrical problems: is everything that's supposed to be getting power, getting power? (Don't forget this includes bad grounds which are often forgotten.)
All lights coming on, then going out makes me think ignition switch. Will the motor start (or turn over) with the fuel pump bypassed? If yes to either, probably not an ECU issue. In 23 years of wrenching, I've only had one bad ECU (Mitsubishi). The symptom was no spark, but everything else was working. And only three bad relays in all that time (two Mitsu's and one VW). Have seen dozens of fuel pump and ignition switch failures.
A few posts on this topic on the internet as well:
http://www.defendersource.com/forum/...ues-19999.html
Ignition switch issues are also plentiful:
http://www.defendersource.com/forum/...tch-34421.html
61 II 109" Pickup (Restomod, 350 small block, TR4050)
66 IIA 88" Station Wagon (sold)
66 IIA 109" Pickup (Restomod, 5MGE, R380)
67 IIA 109" NADA Wagon (sold)
88, 2.5TD 110 RHD non-hicap pickup
-I used to know everything there was to know about Land Rovers; then I joined the RN Bulletin Board.