Connectors

If you're better working on paper, print figure 15 (or 16 if the car has a rallye cluster) and tape the two pages together. Also might want the accessory diagrams that follow.
Now lets take the connector in your 3rd and 4th picture. It looks like it has a relatively thin yellow wire..

On the wiring diagram look for a small gage yellow wire.
Here's a couple.
upload_2020-9-17_18-24-57.png
M is the circuit, 2 and 6 indicate the segement of wire.
20 is the SAE wire gage (20 is about as small as you'll find carrying power in the car)
Y is the color - Yellow.
So your connector is most likely a part of the return for the dome light and any other interior lamps. Grounding any one of these yellow wires completes the circuit.

Here's a connector on the accesory diagrams that looks like it might be a candidate for the one in your last photo.
upload_2020-9-17_18-44-7.png
And it looks like 'M' identifies wires related to interior lighting.