Hey Everyone. I've been a 3rd gen owner for 20 years.I bought a GTA 89 Trans Am 7.5 years ago and slowly working on it. Previous owner did a typical mess of the stereo wiring and I'm trying to clean it back up to factory connectors.. Long story short, in my studying over the weekend، I learned that there was a convenience center that has a fuse for what's called a ARC Radio and Vats. My arc fuse was blown so I replaced it. What's weird is that my orange wire still doesn't have 12 volts to it. But I have a orange/black wire that does!! And it loses 12 volts when I remove that Arc radio fuse. I realized that I have 3 wires I don't know about according to all the research I do!! I have this orange/black that I've never seen in my other third gens that I can remember, and 2 black/blue wires sitting there snipped. And then my orange wire which i thought was the 12 volts constant but apparently not. So these 4 wires got me in a pickle? The bundle of wires they come from don't look like they have wires snipped and these wires are just sitting there?
any idea why my orange/black wire is 12 volt constant and not orange?
I got a book for an 88 firebird that has the entire car build, and it seems like there are variations for subs and UK for wiring. Anybody seen this or know what those black/blue wires are?

 

A lot to unpack here,
-I really can't speak to a Euro spec. wiring, sorry
-I'm assuming you have an aftermarket radio? Two things that can cause a fuse to blow are a short in the circuit and a over current state. Typically fuses don't fail on their own, do you have a amp and sub type of system? the ARC fuse is for a factory stereo to keep power to the radio for the radio presets and clock, I've read that some with aftermarket stereo's bypass this fuse, the constant 12 vdc should be protected someway ie. a fuse.
-What happens when the RADIO fuse is pulled?
-Have you checked for 12 vdc on the red wire feeding the ARC/VATS fuses?
-Is there anythng else that isn't working? The ARC/VATS fuse is feed from a fusible link that should be terminated at the starter, this fusible link also supplies power to the ignition switch.
-PWR ACC circuit breaker is fed from the same fusible link as the ARC/VATS fuse, and issues with power Iocks, mirrors, interior lights, and cigarette lighter?
-The ORG/BLK wire, does this go back to the fuse block? ARC fuse? Check for continuity between this wire and the ARC fuse?
-The BLK/BLU, does your RH rear speak work? If it does are you able to isolate the spear with the fading function on the stereo? The wire schematic below shows a DRK BLU and LT BLU wires associated with the RH rear speaker
Wayback Machine (archive.org)
Wayback Machine (archive.org)
-Maybe your BLK/BLU Euro market and the US market BLU serve the same function and maybe your ORG/BLK and the ORG serve the same function

Sorry don't have any solid answers maybe what I've brought up will lead to an answer.

 

Here is the wiring diagram for the 88 GTA specific UT4 radio: