Pete Zahut

So he was, sorry, 'my bad' as the Mercans say.

Well, as Herbie says above:

This should help:

That dash cam is way too low and just screaming for some bored Plod to walk past it to aid him in his daily targets.

The bad capacitor issue of LS400 ECUs is very well documented and has a range of dozens of possible symptoms, so you really need to bite the bullet and get that done first to give you a stable baseline to work from.

So let me get this straight. You pull out the 15A Dome fuse from the "main fuse box" - where is this main fuse box? You seem to think that this 15A fuse feeds the whole of the fuse box in the driver's footwell Is the fuse box in the driver's footwell the same as the picture that @runsgrateasanut has posted above? If so, there is absolutely no way whatsoever that a 15A fuse can be supplying the power to that whole fuse box and all the devices it feeds, so you need to do more investigation.