You're not missing any wires.
jamesinc your lights probably do not need replacing. They look immaculate. These lights are notorious though, because the plugs don't make good contact with the flexible circuit board on the back of the lights.
I think to help make sense of it, you should go look at the wiring diagrams, which are here: https://ozvolvo.org/archive/?book=bae180116f on page 17.
Left taillight
In the photos I can see your left tail light connector has the correct wires ✅
Right taillight
In the photos I can see your right tail light connector has the correct wires ✅
So you aren't missing any wires, and most likely what is happening is the connector pins are fatigued and are not making good contact, OR the bulb holders themselves are not making good contact.
The easiest way to navigate this is with a multimeter, it will show you whether the problem is the connector or the bulb holder (or both).
