The radio wiring in the VW T5 and T28, at least for the 2008 model year, does not have an ignition switched live feed.
It's easy enough to buy an adapter from the Quadlock plug to the standard ISO connectors, but they will have one or two wires not connected to anything. One is for power on and the other is for the illumination. The simplest, and an acceptable, solution is to connect them both to an ignition live feed.
From what I can find on the internet, there are a couple of places to get this feed.
A possible location is the Anti-Slip Regulation (ASR) switch, which is usually near the radio. The trouble is, I could not find any details of the wiring, so I do not know what current rating the feed has, nor what fuse it is attached to. I could have tested the wires to determine which to use but I'd rather a known quantity.
The other suggested option is Fuse 19, which I prefer.
Fuse 19
This is Fuse 19 in the top fuse box. That is designated for, among other things, radio and navigation systems. It is a mini 5A fuse.
To get to the wire, it is necessary to remove the passenger side dash panels. This is a few screws and a couple of pull off panels. An easy job but takes a few minutes.
Once the panels are removed, the top fuse box can be unbolted and I found there was just enough slack, that with a little care, I could slide it out sideways and have good access to the rear cabling.
Fuse 19 is one of the tiny fuses in the middle. 4th in from the right. The feed comes in, from the ignition, on a brown/green wire and exits on a brown/red wire.
I spliced into the brown/red wire.
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