I assume you have air con ?, if you don't the fans are single speed.
The mere fact that the fans operate suggest a major fault is logged in the ecu, as this is safe mode, it will also bring on the fans if you disconnect the plug for the ecu cts with the engine running, but stop when replugged.
Has the battery had any knocks ?, a broken bit of plate can cause this, as it moves under the rest of the plates in the cell it causes a short, which can cause the speedo to jump due to a voltage spike, as alternator tries to overcome short, but another corner, bump etc and the bit moves, so does the short.
Pure luck where it is when it comes to a stop overnight.
Rare but does happen, my dad had one, oddly enough on a mondeo as well, with a battery from wilco, who kept refusing to change as always registered ok by the time it was at the shop, but was defo faulty, and of course the fault went when the battery went and got replaced.
The other suspect I'd be looking at is the alternator, even though charging correctly the diodes(one way electrical valves) can be leaky.
tabetha