Sorry to read about your various health problems.
With a freshly charged battery and the ignition switch on, the entire electrical system is closed to dead. The lights are exceedingly dim, even the red oil pressure light is exceedingly faint.
You might or might not have to disconnect all the electrical connectors again to clean them. Ime, unless your garage suffers badly from condensation, insulated electrical connections won't corrode badly for many years, especially as you'd fitted them with dielectric grease last time.
What you've described are several separate circuits with the same problem, so I'd look first at parts of the harness that are common to more than one circuit:-
. I've come across a bizarre error(?) is some Lucas
harnesses - you can trace a Red wire from almost every electrical component to a ring terminal on one of the head-steady studs, but not from the ring terminal to battery +ve. There is a Red wire from battery +ve to somewhere else on the bike but it means the electrical return path for all the components is from the head-steady stud through random bits of bike to the other Red wire ... corrosion between the random bits of bike will affect the electrical return path ...
If you have a multi-meter, use its Ohms function to check first there's a good low-resistance between battery +ve and the head-steady stud with the wires on, then try a few checks between battery +ve and different components, ensuring the meter shows the connections as low-resistance throughout.
. If having good low-resistance connections between components and battery +ve doesn't improve the electrics, turn to those between battery -ve and the ignition switch, in particular the fuse and its connections. If the fuse is the standard glass cylinder with metal end caps enclosing the fusible strip, I'd replace it as a matter of course; if you want to replace with the same, use a US 15A or 20A (not
35A) but replacement of both fuse and holder with the more-common automotive blade is a good idea.
. Check the wiring and connections between battery -ve and ignition switch for similar low resistance as you did between components and battery +ve.
. Similarly, check for low resistance across the ignition switch contacts, using the meter connected to the input (Brown/Blue wire) terminal and the Brown/White (lighting switch supply) and White (all other components supply) terminals.
Fwiw, I'd try to solve the electrical problem(s) first; the bike might have carburation problems also but, with an electronic ignition fitted, your "first issue" might be another electrical one ...
When the bike is good and warm, at idle the oil pressure light comes on. I have a Triples Rule oil pressure gauge currently on the bike. The pressure drops to near zero when the bike is at idle.
As others have posted, regrettably this might indicate the need for a full engine strip and remedial work.
However, before doing this, check with another gauge - like most things, gauges aren't immune from failure ...