Electrical question - reversing lights

I changed my gearbox and would like to hook up my reversing lights.

However there are 11 available prongs on the loom plugs that went into the old gearbox and I don't know which two to hook up to the new reversing toggle.

Five of those prongs are grounds, one has 10V when the lights are on, and one has 10V when the ignition is on.

I thought I would use the multimeter to detect continuity between the power pin that the reverse-light's bulb plugs into, and see which one of them had no resistance to the loom plugs.

But it turned out that BOTH of the pins that the bulb plugs into, are connected to ground (they have no resistance against the chassis). This doesn't make any sense to me and I don't know how to progress from here.

I suppose it could even be possible that there's no direct connection, eg. the gearbox has to tell the ECU it's in reverse, and then the ECU activates the lights, or something. The wire colors on the bulb plug don't match the wire colors on the loom plugs.

I also noticed that some of the other pins on the loom plugs would be ground when the ignition was off (ie. no resistance to the chassis), but not be ground when the ignition was on. How does this work? I was expecting that things are always either ground or not, and if the ignition was off, they would simply not be connected to anything.