Haven't added any updates to this thread for a while, mainly as I didn't undertake anything worthy over the winter but I think I've finally got to the bottom of an annoying electrical issue, that I've had since owning the car and a more recent electrical issue.
For three years of ownership, I've had the dash warning light come on, quite regularly, for error code 23, which is the front knock sensor. As I documented here in this thread, I replaced both knock sensors last year. Problem never went away. A few weeks ago having put the car back on the road for the summer, I started to investigate further. After a few emails to Kaz for advice etc. and doing various continuity & voltage checks at the two connector ends of the harness that connect the main ECU & knock sensor sub-harness, I found that the voltage to the front knock sensor was virtually non existent, 0.03v compared to the rear at 0.2v. The reading was the same at the ECU output. Conclusion was the ECU was faulty. Not sure where to go for repairing it, I asked a guy at work, who's the electrical specialist in one of workshops. He said he'd open it up and check the soldered joints, before I took it to a specialist ECU repairer.
He couldn't find anything significant, just some small cracks around some of the joints, so he re-soldered them anyway. He also did the same for my cooling fan control unit, as I've had the odd time where the radiator fan wasn't coming on and the temperature gauge getting a little too high for comfort. Another particularly annoying issue, as I've replaced what I thought was the cause, the coolant sensor into the engine but two years later, the problem re-occurred.
The good news is that both repairs seemed to have worked. The knock sensor warning hasn't come on in the last two journeys (it usually come on after 5 minutes of driving) and the cooling fan kicks in when it should.
The annoying thing is, I changed both knock sensors unnecessarily, keeping what I thought was the only good one and throwing the faulty one away.
I'm beginning to come to the conclusion, having had these issues and doing quite a bit of internet searching for NSX electrical issues, that the electrical units, that seem to give most issues, are mounted directly to the rear bulkhead panel and due to their ages & probable vibration issues, being closer to the engine, could be the cause of many annoying electrical problem, the main ones being, main relay, cooling fan ECU and main engine ECU issues. This is just my opinion but I shall certainly look to these areas for any future issues I might have.