In truth, it would be impossible to inform you of what you have. What were these cables attached to originally. Your subject says REPLACING, so you most be replacing something.
If cables were not attached to anything, then you need some test equipment to determine what you have. Also no mention of any earth cables??? If there is no earth present, you must not connect class 1 metallic fittings.
I would guess when you say yellow you mean green/yellow, and I would guess one cable goes to switch and one is supply, so likely one wire on each cable connects to a wire on other cable without connecting to lamp.
The problem is we don't know which wire, so some testing is required.
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