Cabriolet radio install
Installing a modern radio in an older VW presents a unique problem - there's no switched power. The stock radios are active all the time, whether the ignition is on or not. This doesn't work so well with modern stereos, which are never really off unless the power is removed from their "switched power" wire.
The usual solution is to take power from another switched circuit - say, the defogger switch, which is conveniently nearby. This works, but you lose the ability to listen to the radio with the engine off, because VW ignition switches have no "accessory" position.
I chose to take advantage of the "key-in" contact on the ignition switch. This contact is normally used by the warning module to make annoying noises when the key is in and the door is open. (This module is commonly missing, yanked out by annoyed owners; my car is no exception.) Key in - radio comes on. Pull the key out - radio turns off.
I can't be the first person to have this idea, but I've never seen it documented anywhere, so I thought I'd share the wiring diagram. This is valid for at least '85 through '89 Cabriolets; I suspect it will work on any car where VW used this particular seatbelt warning module, which knowing their penchant for parts reuse, is probably most Mk1s and likely a lot of Mk2s as well. Wiring diagram behind a cut so as not to mess up anyone's friends list:
The usual solution is to take power from another switched circuit - say, the defogger switch, which is conveniently nearby. This works, but you lose the ability to listen to the radio with the engine off, because VW ignition switches have no "accessory" position.
I chose to take advantage of the "key-in" contact on the ignition switch. This contact is normally used by the warning module to make annoying noises when the key is in and the door is open. (This module is commonly missing, yanked out by annoyed owners; my car is no exception.) Key in - radio comes on. Pull the key out - radio turns off.
I can't be the first person to have this idea, but I've never seen it documented anywhere, so I thought I'd share the wiring diagram. This is valid for at least '85 through '89 Cabriolets; I suspect it will work on any car where VW used this particular seatbelt warning module, which knowing their penchant for parts reuse, is probably most Mk1s and likely a lot of Mk2s as well. Wiring diagram behind a cut so as not to mess up anyone's friends list: