Hi, while searching for the fuse for my radio which isn't working(I thought that original Clarion unit from 1997 was faulty,so I replaced it), I came across a 3 pin connector,the same one that is in the engine bay.This one is under the dash and is connected to the same wire that splits and goes into the radio. Is that ABS diagnostic or something else? Forgot to say my Coupe is 2.0 16v,was 1.8 but got swapped because of blown engine. Here is the photo of the connector. https://imgur.com/a/fA98Rs7
Also off topic,hopefully someone can guide me why radio isn't turning on, I couldn't find any fuses for radio in the fuse box. I didn't mention I also replaced the front speakers because they were falling apart(and probably didn't also work).

That's most likely, given its position, the airbag ECU diagnostic connector.

The problem with your 2.0/1.8 hybrid is that here in the UK we never had the 1.8 so we have very little knowledge of the systems. Look for 'services' fuses - there may be two of them - which may power the radio. Also, on UK models, there are often problems behind the radio mounting cradle that can result in short or broken circuits back there. You may have different routing on a left-hand-drive car.

The yellow sleeve is used for the wiring to/from the airbag ECU which is bolted to the floor in the centre underneath the centre console which houses the radio.

As for why the radio doesn't work, check the earth connection, and check that +12V is being supplied, there should be 2 supplies, one permanent live (for radio station and settings memory) and one normally switched live (for when ignition is on). I bought a replacement head unit which also didn't work, then I found the bad earth connection