Hi, Olly.

These loop coil style probe on the handheld multimeter is good for measuring AC but not for DC especially the minute current.
You would need really expensive one for accurate DC current measurement.

Still, we are talking about the dark/parasitic/residual current less than 100mA and in the order of 10mA so best if you connect your multimeter inline/series between the battery negative post and the GND cable.

Before doing so, please double check the current rating of your multimeter.
You may blow its fuse if you have stuck closed power window circuit, AMP relay, etc.

If you have aftermarket security devices, it could be much higher but with factory fitted OEM security or immobiliser, you should see somewhere around 50 - 90mA.

Please note that Honda branded security/alarm systems on UK model with Thatcham CAT1, etc are dealer fitted and not from the factory.
Thus, they will increase the current drain.

If over 100mA, you have extra devices and if it's like 0.5A or over 1.0A, you have serious drain issue.
Very likely to be the case on your NSX.


From what you wrote, the ACG rectifier and regulator are fine at this stage.


Separate issue but you should consider replacing the IGSW cable.
When in P2 ON, both IG2 and IG1 are active.

The gauge unit is powered through IG1.
In P3, IG1 stays On but not the IG2.

Therefore, depending on the ABS warning circuit, the ABS light may rest when turning the IGSW towards P3 START but rest of the gauge lights should stay On.







I have seen people using cheap screw type battery isolation switch (like above photo) installed at the battery negative terminal but personally, not recommended.
The contact current rating is just not enough with these cheap models.
Due to the vibration and the thermal shock, the screw type switch gets slightly loose and repeated process will increase the resistance at the terminal contacts resulting in reduced current flow.
Already seen several NSX struggling to start the engine because of this.










[All photos courtesy of Mr Toyoizumi at T3TEC, Japan]

You really need the race spec spring/pressure loaded switch with enough contact capacity.
Still, it needs replacing at certain interval but far better than the cheap screw type products.

You can find it through Demon Tweeks, etc.

It is designed to be mounted somewhere away from the battery so easily accessed without being disturbed by the spare wheel, etc.
If you know your local automotive electronics or audio shop, etc, they should have thick wire gauge, huge crimp terminal and the crimping tool so ask them to create the required wires/terminals.
You need to be creative on where to mount the SW.

There are several aftermarket products specifically designed for NSX usage as well.
T3TEC has one but not cheap, though better than killing your battery every few months.


Kaz