I just dug out my Bentley for the 1987 GTI 16V, and you just bisected...the wire going to your alternator warning light.
The Bentley shows two wires* going to the alternator: an 18-gauge blue wire for the dash light, and an 8-gauge red wire for power output. Apparently, the field sense circuit is internal to the alternator. So you have one of two choices:
- Wire your car up per Figure 1 above, bisecting your alternator output wire (the red one) through that smaller circuit; or
- Bisect a different wire that will kill the car absolutely, such as the fuel pump or ECU power.
The first option I'm not thrilled with; I don't know if those terminals are rated for the current the alternator could put out.
The second option would work; your fuel pump gets power from a G/BK 14-gauge wire off terminal 33/87 on the fuel pump relay connector; bisecting that would kill power to both the fuel and transfer pumps. The car, obviously, would die instantly.
Alternatively - and more attractive - for option 2 you could bisect the 12-gauge yellow wire off the ignition switch; that's the main keyed power output (circuit 15) that runs pretty much everything in the car (e.g., ignition module, distributor, coil, etc).
On the plus side to your "current" situation (har-de-har), you'll never see an alternator warning light...
Yes, you'll want to reconnect that wire...
GA
* Well, three really: the third "wire" is the ground to the chassis...
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