The simplified circuit diagram here might help...
http://www.volkszone.com/VZi/showthread.php?t=585715&highlight=audible" onclick="window.open(this.href);return false;
It's tricky cos is not what you might think - the circuit starts at 12v and gets switched to earth to complete circuit, you might intuitively think it started at 0v (earth) and 12v is switched in to power the the actual indicators, but that's not how it works....