Welcome to Prime! Need a few more details to help you start with this. Adding your location and model particulars to your sig and profile will help folks here give more accurate help. Are you JDM RHD or European RHD? Where are you located? Guessing EU based on the time of your post? The radio head units were market specific, and I'm not sure you can just drop in the market-correct unit and have everything work perfectly, even if you could find a unit, which is getting very hard these days.
Start by looking up the exact fuse for your radio and then checking for power at the radio electrical connector to be sure it's not that simple. Without your year & market specifics, I don't know the fuses. You'll need a year-specific electrical service manual before you do any work of this variety. 1997+, the stereo is powered by 3 fuses: Fuse 8 supplies the head unit; fuse 51 supplies the dedicated speaker amplifiers, and fuse 33 (clock) supplies constant power to retain the radio presets. Interestingly, the cigarette lighter is on fuse 15, but the ignition-on relay for it is from Fuse 8 - so if the radio fuse is blown, the cigarette lighter (and radio) won't work, but if the lighter fuse is blown, the radio will still work. Since your lighter works, the radio fuse is fine, if your wiring is the same as 1997+, but there could still be a wiring issue between the fuse and the head unit. With the failure rate of the head units after 30 years, that's the more likely culprit.
JDM radio frequencies won't work in North America anyway, even if repaired. If it was working, you could add bluetooth with a GROM unit, but that would mean finding someone to fix your stock head unit first. If you're in the EU,
@Heineken does amazing work. In the US, you'd probably need Wilman's to replace the stereo internals with newer ones, which would include bluetooth. About US$2k? The other option is replacing the head unit with non-OEM, which will also require a new faceplate trim, but be careful, as the wiring to the speakers will need to be changed as well. Also be careful removing the trim, as it's easily damaged and rather expensive.
The other question to assess is your general level of comfort wiring 12V harnesses, and perhaps wiring electrical in general. This won't be plug 'n play and an electrical mixup rewiring things could get VERY expensive, VERY quickly, if you mix up or accidentally short wires. Some components are NLA, so if you damage them, it's quite a pickle. If you damage wiring away from where you're working, that can be very hard to find and often require (expensive) expert intervention.
The NSX uses a less common audio system with pre-amp level outputs from the head unit with integrated amplifiers mounted in the speaker enclosures; thus the wires from the head unit to the speaker boxes are low current and can't handle speaker level current draw. Also don't send speaker outputs from a regular head unit or you'll blow the amps and perhaps the speakers. You'd need to remove the amplifier wiring from the speaker enclosures and wire the speakers directly to your new bluetooth-equipped head unit with appropriately sized wiring.
If all you want is bluetooth, your cheapest and simplest solution is probably a stereo bluetooth speaker. The sound quality won't be great, but the NSX stereo is so-so anyway, especially if you haven't added auxiliary tweeters. The soundtrack is that glorious VTEC engine and the intake sounds! Another option would be a hidden bluetooth receiver wired to the door speakers with the speaker amps bypassed, but you'd be missing the subwoofer and it's audio contribution.
Best,
