I'm troubleshooting the electric oil pressure gauge and sender in my 1970 IIA 88" petrol. I connected the gauge to a 9V battery and it seems to work, but the dark green wire on it was disconnected. I assume it goes to a power source - would an empty terminal on the ignition switch be OK?

The sender is also a mystery. It's got 2 terminals and seems to be part # 537138, based on pictures I've found. One wire runs to the gauge. The other isn't connected to anything. It just ends in a bullet connector. Where should it be connected?

If I have to replace the sender (I suspect it was disconnected because it just didn't work), are there any aftermarket ones that'll work? The genuine Smiths ones I've found are pretty expensive.