I swapped my fully loaded drivers seat from my old Mondeo to my new one, but the new one is going back so put the fully loaded seat back in my old car and since plugging it back in, I'm having the below problems.

The screen in-between the clock just displays Convers+ splash screen, the engine temp shows -60'c, when i push the ignition button it blows the fans on full power for 2 seconds. Also the doors won't lock. The car starts and drives ok but theres a problem with the dash electrics. 

Any idea what's up with it?

Furthermore the reverse camera doesn't show and the parking sensors don't work. There aren't any dings or noises as there usually is.

Took the battery off for half hour, left the seat disconnected, and still exactly the same after reconnecting the battery (leaving the seat unplugged).

Fixed it, seems the two canbus wires were shorting for the seat plug.

But now the entire seat doesn't work, up down, forwards backwards, backrest, none of them work.

5 hours ago, boylin said:

Fixed it, seems the two canbus wires were shorting for the seat plug.

But now the entire seat doesn't work,

Earlier, I was tempted to say canbus error for that odd list of faults, mostly on what is likely to be the secondary canbus (MS-CAN on a Focus). But as I know very little about the Mk4 Mondeo, I kept quiet!

It sounds a bit as if the canbus is now not getting to the seat. I bet there is a bus controlled electronic module in there, with all those motors & sensors. Though it could just be power, of course, but I expect you have checked relevant fuses.

If the seat controls go through the BCM (aka GEM) module, there is a BCM test mode, see: http://www.fordwiki.co.uk/index.php/GEM_Module_Self_Diagnostics

This may help. If it still proves difficult to find the error, Forscan can probe just about all modules on the car. It should identify if the seat module is on the bus, will show any error codes in it, and maybe initiate a self test mode.