Two way radio wiring!

[Hibby]

Hey all!

Been mulling this over in my head recently, figured I'd come on to ask and fill in the gaps in my knowledge - if someone else in future is daft enough to do this, there'll be a resource for them too.

So - I'm installing an Amateur (ham) radio in my (uk, 2004, t2) yaris - long drives are getting lonely and I want to speak to other weird men. Or something.

I've got relevant cabling with adaptors for the battery, proper fusing and have the electronics bit sorted in my head, it's the fitting that I'm looking into in more detail.

I've found a grommet that comes in through the bulkhead/firewall from engine to cockpit (behind the glovebox) and can fit my new wire in this. Great!

BUT!

What I can't do is go any further than that - It's quite tight behind the dash, and my head's too big to fit under there to see what's happening, but I'm pretty sure the wiring isn't breaking through to the good side.

Is this to be expected? Am I going to have to find a way to contort my arm behind everything to cut the carpet and bring the wire through, is there a big plasting thing stopping me from doing this and has anyone any suggestions on how to continue?

It's quite similar to running any form of cable from battery -> cockpit, however my complication is that there's a (not large) adaptor on the end of the cable for attaching to the adaptor near the back of the radio.
This in itself shouldn't be an issue... should it?

Phew. Wall of text.
TL;DR:
Curious about how cable from grommet behind glove box in UK 2004 yaris enters cockpit, wants to know more.