Mk1 Focus C-Max 2006 2l TDCI

Strange fault:

Heated Windscreen does not work which I suspect is related SOMEHOW - please bear this in mind.

I changed the relay for the heated windscreen last Friday and within an hour, I had the strangest electrical fault I have ever seen happen to me

All my dashboard gauges were ready 15% or so HIGHER than the actually were and even had a reading with the engine OFF and car parked - and yes, ALL gauges were affected.

After several restarts, the issue seemed to have solved itself but the car acted like the ECU had been reset and error codes erased but it still had the engine management warning light ON

I then found that I had ZERO acceleration - even less than the car has with the P2455 error I currently have (This is being investigated and looks to be an ECU issue).

Here's the kicker, I removed the replacement relay the following day and the car responded normally for the day - except for the 500yds I travelled when I tried putting it back in again (loss of power again).

So I finished the day without the relay in and put it back in this morning to attempt to defrost my windscreen and the car is responding perfectly now (excluding the P2455 error that has been there since I owned the car - limp mode enabled).

I suspect an earth leakage somewhere is the initial cause of the error. Any theories as to where to look at all? Could it be something to do with the relay itself that is causing ALL of my issues (including the 5v feedback up the DPF sensor wire that is triggering P2455 error) or is it more likely to be a loose connection somewhere causing glitches that are actually unrelated?