Tacho, OBC and interior lights

[mcspike]

Hello

Been having intermittent troubles with the bits in the topic title. They come and go in a very illogical fashion.

I have tried a different instrument cluster which it both worked and failed with.

The OBC backlight will continue to be lit even when nothing is displayed on the screen which is linked with the tacho dying.

The interior lights (LED) will occasionally work VERY dimly with tacho etc. and also at full brightness.

I fixed the original cluster back in properly yesterday and went for a short drive. Everything was working when I left but during the 8 mile journey the tacho etc. was cutting out sporadically until I reached my destination then nothing worked at all on my way home.

All the fuses are good. From reading I know all these are on fuse 21 iirc so there must be a fault somewhere.. Loose wires, dare I say?

Any ideas much appreciated.

[Brianmoooore]

First thing to check is the main earthing point behind the RH side of the glovebox. (Where several brown wires converge.)

[mcspike]

Forgive my stupidity, I can't find it. I have removed the two plastic covers on the upper and RH side but nothing seems obvious. Do I need to remove more?

[Brianmoooore]

No. Should be visible just right of centre, right back on the reverse side of the engine bulkhead.

[mcspike]

Tight with 3 brown wires attached. It was hidden behind some cable tied loom...

No change.

Additional information that may be helpful is that I have lithium batteries in the cluster(s) and it started to go much the same as it is now. The car has also had an engine swap, an M40b16 to M42b18. The engine swap went very smoothly with no wiring issues.