Midday Saturday after a bit of overtime I started the 350z up and sat there as it warmed, but, about one minute into my religious warming up before a blast routine she cut out, never done that before, restarted it and 5 seconds in it cut out again, from that point wouldn't even turn over, had a quick check of all related fuses and all seemed intact.
Called RAC and within 30 mins they arrived, after a lot of head scratching he started wiggling the relays in the fuse box behind battery as I tried the ignition and woohoo she started and was running fine, as car happily ticked over I looked at the rogue relay and said 'that's wierd, it has an orange led behind it and is illuminating the back of the relay'............NAAAAAA it was actually one of the prongs melting, engine off, relay out, the relay was rusty behind and the melting prong had rotted through and was arcing across to the remaining piece of prong which was now embedded in it's socket, after a lot of poking around I got it out but the internal contact was too rotted, I got the RAC to take it to my local Nissan garage as it will need a complete new fuse/relay box.
Very strange that the relay had rusted/rotted but not even a spec of dust anywhere else on the fuse board.
I have got to phone the Nissan garage in the morning to get it sorted, service guys where not there when it turned up, won't be cheap but she's my baby.