This is the headlight circuit which is separate from; but, connected to the headlight door circuit. As a result, the headlight doors can operate just fine with dead headlights. The headlight circuit is fairly straightforward, unlike the headlight door circuit which is definitely not straightforward. Be happy that the doors work!
A flaky ground G403 will stop the low beams from operating; but, not the high beams. A flaky ground G201 will stop the high beams from working; but, not the low beams. As a result, it seems unlikely that either of those grounds is the problem. Ground G401 is the ground associated with the light bulb control function and it can kill everything. Check G401 which is the black wire coming out of the lighting switch.
You said you tested 'both sides' fuses. That is confusing because there is only one fuse for both sides. There are separate low and high beam fuses #52 and #49 if that is what you meant. If not, check those two fuses.
If the G401 is good, then I think you need to do a function test on the lighting switch. The low beams and high beams get powered through the lighting relay which is directly controlled by the lighting switch. When the lighting relay is energized the low beam always come on The high beams get switched on by means of a separate ground path controlled by the dimmer relay. Given that you have random operation of the headlights, if G401 is good then I bet that you have an intermittent or dirty contact in the headlight switch that controls the headlight relay.
Page 23-177 of the service manual contains a pin out diagram of the connector for the lighting switch and a switch terminal connectivity table which will allow you to confirm the operation of the switch. Note the diode indication in the connectivity table. In order to check the switch operation you must have the - lead of the tester connected to the cathode side of the diode (in most case terminal 1 - the black wire). Do it backwards and the switch will always show open circuit. You can get a copy of the service manual from the NSX Prime Library
As our NSX continues to age, it will become more and more important for member to be able to service their cars. Most Acura dealers no longer employ technicians who are familiar with the NSX, as the original techs are long gone or retired. As...
www.nsxprime.com
Edit
Just for clarity, I should have included this diagram which is 'mostly' the retractor control circuit. What is relevant is the little area shown circled in red which is part of the headlight switch.
What is significant is that the headlight switch knob actually controls 4 separate sets of switch contacts. Two switches control the light bulb and tail light operation and two switches control the retractor operation. The part of the switch that controls the headlight relay circuit can fail and still leave the tail light and retractor doors functioning fine.
You did not say anything about tail light operation. Do they work OK?
