The chime relay is missing in my 1988 928s4 euro. I finally got a chime (gong) relay for the car, and

Mounting the relay is VERY simple. Very unlike anything else with Porsche ;-).

1. lower the driver seat all the way. You can access 1 screw that holds the driver-side panel of the center console. (LHD...)
2. unscrew the other screw that holds the panel, and take it off horizontally into rear direction. It slides a bit over the under-dash tray.
3. take the black controller box (central locking) off by removing the screw that holds down the mounting bracket.
4. you will see two relay sockets next to each other, just behind the ash-tray and clock. The one to the front is the one you're looking for.
5. the left socket may have a jumper-plug inserted that you have to remove. Probably to fool the safety-belt warning light.
6. insert the relay in the left (towards front) socket
7. turn on the parking-light to verify operation. A 'gong' should sound.
8. close everything up again in reverse order.

The gong sounds when the door is open and lights are on.

The gong sounds when the door is open and ignition is switched on.

The safety belt warning lights up in the dash for 5 seconds.

Easy job, takes 10 minutes.