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Uwe, a VW expert who will remain nameless, and I have discovered a problem
with using a Metra wiring adapter when installing an aftermarket stereo in a
'98 GTI-VR6. I will try my best to explain the problem here. If you are
planning to install an aftermarket stereo in your '98 car, please keep
reading.
I bought a wiring adapter for an aftermarket in-dash CD player at my local
electronics superstore (Circuit City) the other day. It's made by Metra and
the package says "VW, 1987-up." It's got a square black receptacle on one
end, into which the factory harnesses plug, and loose wires on the other
end, which get connected to the wires from the radio.
If I were to hook up the new stereo to the Metra adapter according to
Metra's instructions, my radio's antenna lead (12v) would be connected to a
constant 12v wire on the factory side. This is not good. And get this: the
Metra adapter has a wire that links the radio's antenna lead (which is
already in the wrong place) to the K-wire on the factory side. (The K-wire
is linked to the ECU and allows a VAG 1551 to interface with the factory
radio. This wire should remain OPEN if you install an aftermarket radio.)
Let me try some ASCII art to illustrate. I'm going to focus on the bottom
half of the receptacle on the Metra adapter because that's where the factory
harness with all the power wires plugs in. (The top half of the Metra
receptacle receives the factory harness with all the speaker wires.)
1 3 5 7
open ant ant mem
|_____| (wire connected to #3 and #5)
2 4 6 8
open 12v dim ground ("Dim" is for dimmer)
(switched)
The metra adapter actually has a wire that jumps from pin 3 to pin 5. There
is another wire coming from pin 5 that is supposed to be connected to the
radio's antenna lead.
Now, on the factory harness, pin 3 is the K wire, or "data link" and pin 5
is "Positive (B+) supply (anti-theft)," according to the diagram that Uwe
kindly posted at
I'm no electrical engineer, but this looks VERY wrong. I tested pin 5 on the
factory side and found 12 volts constant power (regardless of whether the
key was in the ignition or if the ignition was on). Now, imagine that power
getting routed to the K-wire (by the Metra adapter). Then, throw in the 12
volts coming from the radio's antenna lead. Is this a recipe for disaster,
or what?
Uwe wrote:
>If an aftermarket plug-in harness connects the K-wire to something it
>shouldn't, then that may explain why the dealers are seeing blown ECUs.
>If this is the case, it sounds like someone mis-engineered the
>aftermarket harness. Ouch.
Bingo. Either Metra has not updated its adapter for the 1998 cars or they
are not aware of the new K-wire. Whatever the case may be, the adapter
that's available in stores now is downright scary.
Uwe wrote:
>I'll repeat. If you replace the radio with an aftermarket unit, make
>sure the K-wire in the factory harness does *not* get connected to
>*anything*.
I hope this makes sense. If you're putting an aftermarket head unit into a
'98 car, BEWARE! Contact me at jaymart erols for more info.
-Jason
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Tue Aug 25 10:02 CDT 1998