Well I got around to fitting the new head unit this afternoon without any sparks/cuts but a bit hassle - took me just under 1.5 hours of faffing based on the clock adjustment when I'd finished.
Here's my experience/notes to help anyone else
Removing the standard cassette Clarion head unit.**************************************************
It was a Clarion ARX7370R (or maybe a ARX7370RW as the "only difference is colour" but doesn't say which).
I had the instruction leaflet and the removal tools (big aren't they!).
I used masking tape to mask off the fascia all around the head unit BUT THAT WAS A MISTAKE - as removing it caused three small areas of the fascia surface to come off on the masking tape
So don't copy me there!
Took off the removable front; and unclipped the grey DIN hole shroud; inserted the clips (angling them OUTSIDE the visible metal lug at each side, as per leafet) and they clicked home firmly and then pulled radio forward but lots of cable resistance.
Looking round the back. There are some YELLOW wrapped wires down the passenger side that have NOTHING to do with the radio.
There is also a bulky bundle of wires from the top left of the Clarion, all wrapped in grey foam, that are the RCA connectors for external amp etc - ie they are captive cables from the radio and not connected in std Coupe.
There are FOUR cables that ARE connected car<=>radio and all seemed to come from driver footwell corner:
- a medium grey aerial cable by itself
- two ISO speaker & power connectors (bottom right) heavily/tightly wrapped together in grey foamed tape with a 10A fuse alongside it
- a thicker round cable ('DIN' connector, alongside the ISOs)
There was precious little slack on any of them but by coaxing them a bit from driver footwell, and pulling the radio managed to get the unit out enough to get them undone; the ISO ones proving particulary hard to unclip.
Removed, carefully, the old DIN metal frame.
Fitting new £40 Aldi Tevion CD/MP3/Aux/FM/LW/MW head unit ********************************************************
Had no use for the DIN 13-pin C-Bus input cable so masked off the end and taped it down to the top of the ashtray moulding out of the way.
Fitted new DIN metal carcase and bent metal retainers back until seemed firmly gripped. Used a thick Allen Key to give me the right angled leverage to bend the metal tabs.
Connected up the ISO connectors to the 'fused ISO adapter cable' on my new unit - but that DID mean there was a lot of cable/fuse/connectors around the back which proved an obstacle to pushing back the new unit, and had to manoeuvre the cabling behind the unit carefully and pull the dual ISO connector out at the back [there's a rectangular hole in the frame there] to some extent to get it all back.
The first time I connected it up I made the mistake of fitting the unit rather than just testing it while out. For some reason the head unit wasn't recognising the power, but when I used my new extract keys and got it out again and got my voltmeter out and tested the ISO was getting 12V on the standby/memory AND power lines (with ignition off, ie as anticipated based one what we know about Coupe wiring), the head unit suddenly came back to life so all was well (for now anyway).
Sound quality seems satisfactory and all the features I've tested so far seem to work - the most important option being the one being to STOP traffic/news interruptions of broadcasts.
Playing CDs in the car seems so novel and can have 12s or about 48s lag to cope with 'rough roads' too!
Lessons/confirmations/warnings for others********************************
1. I did disconnect the battery negative terminal as advised
2. DO NOT use masking tape to protect the console fascia
3. Std Coupe has the std ISO power & speaker connectors though rather short ones
4. DO wire up and test the new head unit WITHOUT fitting it
5. Watch out for all those (new) cables!
Haven't tested my new Radio's Aux in and the USB & SD memory card slots yet but fingers crossed. Hopefully the car's battery won't be flat tomorrow....
No idea what the Coupe used to tell the Clarion on the 13-pin DIN C-BUS input.