How do I wire up buzzers to rear indicators?

[bizarro]

I'm not the first to mention this, but my '08 Yaris has very quiet indicators and the sound is easily missed under road noise etc.

Somewhere I tracked down some buzzers which can be fitted, and bought some (from here).

There are two supplied in each pack, and the idea is to tap them into the wires powering the two rear indicator lights. Problem is, I cannot work out which.

In the photo (apologies for the quality), you should be able to see two pairs of wires: green and black, and yellow and white. The first pair are just underneath the indicator pod, and seemed to be the best bet. Nope - tapping the buzzer in here resulted in a noise every time the brakes were applied. Tapping in to the yellow and white produced no sound at all for any of the lighting functions.

Has anyone succeeded in doing this, or can tell me which wires to tap please?

Thanks.