Right guys, thanks for all the input. all i can say is the plot thickens!

Gold star to Richie for making me go back and check fuses.

I had previously checked all fuses EXCEPT inline rad fan fuses as these have no relevance, or so i thought..
removed and replaced the two old corroded fuses, cleaned and wd40'd it all up and it fired straight up!!
So i decided to see if it would run without the fuses in, and it does

so basically even though its now running I dont feel like ive got to the bottom of this at all.
The fan loom was made by the previous owner, but all i can say is it runs from the battery, to 2x 30amp fuses (see pic) down to 2x relays, then off to rad temp sender and to rad fans.
Baffled as to how cleaning up the dry connections on a fan loom could stop my entire electrics go nuts?