I have an 87 s4 WITHOUT the alarm but i have found where it was supposed to be wired in. The factory has a couple of jumper leads on a the connections.
If i forget, please remind me and i will dig up the pictures i have. It may help.
You got to go read Nichol's tips more closely.
http://www.nichols.nu/tips.htm . Under 'Electrical -> Alarm Control Unit'.
The only thing I would do differently would be to jumper pins 15 and 87a instead of 30 and 87a. Pin 30 is live even with the key out of the ignition, while pin 15 is live only when the ignition is on. So, with pin 30 jumpered you will have the EZK relay energized all the time and it will eventually drain your battery.
This is the Hella Alarm controller as used in the 928 up to 1990 (ans was then replaced by the Megamos controller)
Alarm bypass wire
Place a bridge wire in the Alarm "relay"
in the center console below the Radio. Bridge 15 to 87a. Bridging to 15
means power is off when ignition is off, which is what you want.
There are two boxes for the alarm. You need to adapt the one with 10 pins.
Plans is to connect the Red-Black wire wit the Yellow wire.
This way the EZK still gets the "go" signal.