Just replaced the stereo in our 07 VW Passat with a JVC head unit so I can get DAB, Bluetooth, USB connection etc, got an iso adaptor for the wiring, aerial adaptor, single din fascia adaptor. All went in well and great sound, much better than the original unit. One issue though, the unit only turns on and off by itself, it’s not linked to the ignition, which I’d prefer particularly so it goes off when you take the key out or on when you get in and put the key in. I put exactly the same unit in our other car (Honda)for the same reason and it’s fine, turns on and off via the key. What’s different about the VW? Presuming I now need to find a live feed on ignition circuit somewhere to connect to the units red power in wire? What’s weird is the original unit did turn off and on via the ignition so I would have thought it would be the same. Confused, any advice appreciated. Cheers

See if there is a menu setting in the radio to enable that function (there is in mine).

The first thing I would try is swapping the red and yellow wires on the ISO adapter (wiring loom that comes out of the headunit). You should see that they have connectors in those two wires. One is memory, the other is ignition live. VW’s and vauxhall’s have these wires the opposite way to standard. No idea why though.

As above, try swapping the yellow and red

Your radio is self aware… 😯

Rockhopper – nothing in the menu for this.
woodlikesbeer & P20 – yeah tried this already, we had a Polo a few years back which lost all the presets everytime the unit was on and swapping red/yellow cured it and memory was retained, but this always worked off the key no problem.
I’m thinking there’s something weird about this VW wiring and the original unit as there are 2 extra wires I haven’t seen on other cars before, small brown ones going from the car to the iso (power/earth) block which don’t go anywhere now, nothing on the new unit block that connects to them. A multimeter shows these are constantly at about 2 volts. The red and yellow main wires are constantly at 12 volts whether the key is in or not i.e they can’t be linked to the ignition power which explains why the new unit has constant power and can only be turned on and off on itself. I’m thinking the only solution is to run another positive feed off something linked to the ignition, like cigarette lighter. If only things were simple like the Honda…

Those brown wires may be to the car’s CANBUS network which passes speed info back to the radio and some data from the radio to the MFD in the instrument cluster.

Of your red and yellow… one wire should be permanent 12v and the other will go on / off with the ignition. Note that it may not actually shut off until the key is removed.

If you’re measuring them both at 12v with the ignition off you’re not measuring it properly.

(I also changed the radio in a VW Passat, had to swap the red and yellow wires).