I bought a '64 - 109" that is on a '99 Disco 2 frame/running gear.

Has the Disco 2 dash and wiring harness/computers.

It starts and runs fine.

Has head lights, brake lights and rear tail lights.
Left rear signal light only comes on with 4 Way Flasher.

No front or rear right signals, flashers in fuse panel don't even "click"

Also no front marker lights.

Tach and fuel gauge used to work until you turned on headlights, then they would go out but would work again once headlights were shut off.
Now they both don't work at all.

Now I also get the Transmission "M" & "S" lights flashing when running.
A week ago they didn't come on?

My generic OBD2 reader doesn't work, it only displays "Error"
Its not the reader as it works in my car.

I just ordered a Foxwell OBD2 reader for Land Rover so maybe it will tell me????

Yes, I have checked all fuses and relays, all plug ins in all computers and all grounds.