Hi.
Well I have had the fuse box out and the relay that controls the fan and the power socket is a Red one on the bottom row on the far left. To gain access you need to unclip the plastic cover from the fuse box after removing the front cover from the box. one cable tie needs to be cut from the cable form at the top. Two plastic lugs hold the actual fuse box assembly into its plastic casing, flexing the casing away from the fuse box and it just pulls up. There is sufficient cable to turn the box round to see the connections and crimps.
The fan was working once I pulled the box up and I reconnected the battery earth and left it on on position 4 with the engine running, after five minutes it stopped. The relay was actually quite hot at that point so a look at the voltages confirmed either an intermittent connection or faulty relay. There was 14v on one thick lead, zero on the other (Both Grey with a grey tracer), 13v on the one side of the relay's coil connection (thin White) and zero on the other (thin Black) that is correct. A little poke on the relay and the click could be heard and the fan re-started.
I removed the relay and took it to the bench, opened it up and the contacts did look a little charred, the coil read 79 ohms. I've cleaned up the contacts and sprayed them with contact lubricant, cleaned all the pins and tightened the connectors in the fuse box.
All working now and if it fails again I'll try to order a new relay.