Rover owners: A slightly different Pektron fault thread.

Hello.
I have recently come by a rather nice condition MK2 Rover 25, but it has some issues I am hoping you can help with.

I've searched this and other areas of the internet, but have not found anyone else with this particular fault.

The car was left to stand with a flat battery for a couple of months (possibly more) by the previous owner.
Upon replacing both the car and fob batteries, I discovered that the fob didn't do anything.
I have tried numerous re-pairing/syncing ideas that I have found in forums etc.

The immobiliser LED was not lit, until the ignition was turned, when various dash lights came on, and there was a dual tone from the SCU. The LED then stays on solid until the ignition is off.
Engine does nothing, no starter, as would be expected form an active immobiliser. When the key is turned to the position that lights the dash, the courtesy light came on for a half second then went out again.

The hazard lights only worked when the ignition was on, and the horn did nothing at any time (fixed now).
Windows appear to work fine,

I checked the boot wiring and some repairs have already been carried out as some point. Some other bare wires have now been covered/repaired.

The ground points have been checked in the engine bay, the front ones having been re-seated by myself on a freshly sanded piece of body (just above the original site). The connectors themselves have been cleaned up as well to insure good contact. The ground under the fuse looks fine, and is solid.

I did notice that there was some white corrosion on the SCU board, so I am assuming water damage. So I have got my hands on a matching, working ECU/SCU/FOB set and installed it.

Having followed Technozens instructions on installing SCU, then battery, then fuse I am still having no luck.

When I plug them in as suggested, there is no beep from the SCU, and no light on the dash.
No response to the fob.
When I turn ignition on, the cabin light flashes once, the alarm light comes on for a second. I get one beep from the SCU and nothing else happens.
There are a few clicks from relays in the engine bay.

Interestingly, it does exactly the same with the fuse removed. I can only assume that there is something else at fault here, failing to provide full power to the SCU or ECU?

I have checked all fuses in the engine bay, and also under the steering wheel. Where I found fuse 1 to be blown. Replacing this allows the horn to sound.
Hazards also worked, both with and without ignition, but seem to have stopped now.
The dash locking button does not function in any state.
The yellow relays in the engine bay have also been tried in several different positions and orders to test for a fault there.

I have also tried the original SCU, with the new ECU. This gives the same error as above, but also the dual tone. Again, with and without the fuse in place.

There is no EKA with the new ECU/SCU, but entering a random code does not sound the beep (or allow the car to start). I have the OLD SCU's EKA, which also didn't work with the old one.

I hope you are able to help, as I'm running out of ideas