Well that is on a skyline I'm pretty sure (R32?) but I think I have found the Stagea one, I think it's the black connector (jumper) under the driver's side dash, on the firewall, at the bottom, to the right... sort-of at the back of the driver's side kickpanel... I will take a photo sometime.
Basically I believe the purpose of the jumper is for bleeding the ATTESA system without having to have the engine running. I think it works like thus:
- turn ignition on, but don't start engine.
- remove the jumper.
- the attesa pump starts and holds a constant pressure in the attesa hydraulic system, allowing for a very easy 'one-man' bleed operation where you only have to open the bleed valve(s) and let fluid out.
As I say, I only think that's what happens, from other members' advice and from reading sites like that one... but I reckon this is pretty close. I'm going to try bleeding mine as the clicking is getting worse and is annoying. It could also be doing harm. Fault codes say 77, which I think is the pressure switch. The manual shows that being integral to the pump assembly, just in front of the pump/diff. But there may be a wiring problem; hopefully just a fouled connector, perhaps from when they did my underbody cleaning at quarantine.... well I can hope.