You said battery terminals were OK, I'd take them both off and give them a good clean, doesn't take much to cause a high resistance...

Also connections to jump start terminal on bulkhead...

Good luck with it...  Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand Sold
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Sold
2002 L322 Vogue 4.4 V8 Epson Green (Fatty Offroader) Sold
-Click for Project Fatty off roader-

Oh for the good old days when you got a big red light come on when your dynamo/alternator packs up / drive belt falls off. Suffered the same problem on my P38A at a set of traffic lights in rush hour one sunny evening. .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Mine did this a few times when the ignition switch went no lights or any thing when turning the key !wiggling the key as you turned it could sometimes get it to work ,

Went back with some spanners and a torch at 11pm last night. Wiggled all battery connections, etc. side repeater light was still glowing orange strangely enough. But absolutely no power to anything else including hazard lights.

So got my spanner onto the neg lead nut and started to unscrew. As I did, I touched the pole and the nut and had a little spark ....... Everything burst back to life! Got inside and interior lights are on; start ignition sequence and all lights are green go for launch Then....

Clunk. No turnover, all lights off.

Flat battery thinks I, so back outside to remove the neg lead and come back in morning with a power pack........ Same happens again ... Spark across the neg pole and spanner.... Bursts into life again. This time it starts perfectly and I get in and drive home, arriving around midnight. went out today fora good run and she behaved like the lady she always wanted to be

Analysis - I have LPG and I think the power take off from the neg lead to the LPG system somehow caused a short or shutdown of the cars whole power system. Not sure how, but the lights on the LPG switch in the cabin were off prior to this incident. This either shorted out or caused a loose connection. Not sure how the spark/short caused it to come back to life tho?

Prize: goes to pete haylands for closest probable cause.