So, I was investigating a problem with my cooling fans and went to check the fuse box on my new-to-me 66 2+2, and behind the centre instrument panel I came across an unattached ring terminal on a green wire. See photos below.
What is this ring terminal supposed to be attached to? I can't identify it on the wiring diagram.
Thanks for any help!
Cheers.

Note the ring terminal on the green wire. It's affixed midway on a green wire, between the instrument voltage stabilizer and where that wire goes into the fabric-covered harness.



The other end leads to the second terminal, labelled "B", of the instrument voltage stabilizer.



Here's a full picture of the whole back of the centre instrument panel, if that helps. The non-original yellow wire and blue connector supply power to the radio.



Here you can see the wire - the tip of my index finger is touching it, and my thumb is against the top of the mystery ring terminal on that same wire.

 

From my reading I gather the 12v system is too high for the gauges that were built for 8-10 volts so that small regulator drops the voltage so the gauges do not read too high. Go figure why Jaguar had gauges built that do not work properly on 12v. Are all the gauges working properly? The length of the wire may be indicative to where it goes.

 

A great many British cars use a voltage stabilizer that delivers about 10.5V to control the fuel gauge and other instruments. This gives a solid, stable, and reliable voltage level which prevents errors in those gauges (allegedly). The voltage on a normal car varies greatly between 12.0 and 14.5 V, depending on alternator output and the state of charge of the battery. As a result, this voltage fluctuation can induce errors in the gauges. The voltage stabilizer is there to prevent that - device will always be able to deliver at least 10.5V, so it can be assured that you will have a stable voltage for the instruments. It’s not that there’s a design fault, or that the instruments are mismatched, this is by design to provide more accuracy.

However, this isn’t really about the voltage stabilizer, my biggest concern is that there’s a ring terminal on a green wire that’s not attached. Green wires carry power when the switch is on, and as a result that wire is not powering something that should be powered, and also presents a hazard because if that ring touches anything that’s grounded, it will almost certainly either blow a fuse or melt a wire.

So… my question is, where does that ring terminal belong?

The gauges seem to work properly, and there appears to be quite a few nearby devices to which it could connect, so I’m puzzled. The large device with all the screws on the back of it is the “PLC” switch that turns on the headlamps and side lamps. Perhaps it belongs there?



On the wiring diagram, I don’t see any green wires that attach to the PLC switch.

 

It looks like your pressure instrument has been converted or replaced by a mechanical unit. So the wire is not needed.

 

Excellent. Just the answer I was looking for. Yes, I would imagine the car originally had an electrically operated oil pressure gauge & sender, and it was replaced by a mechanical unit somewhere along the way. That would absolutely explain it. I’ll shrink wrap the tab and leave it where it is.

Thank you!