here is a post from 2014, the indicator relay with buzzer was just a straight swap with the standard relay, no electricary required, unfortunately cant seem to find one online at the moment.
have fitted one of these, as it is, it is not loud enough so i carefully prised the cover off and drilled 4 holes in the casing, tested it then masked back the amount of holes until i got the right volume. It can just be heard with a sports exhaust and aeroscreens. it also matters where its mounted behind the dash, higher up its is quieter than near the lower edge. Too loud and you sound like a refuse van.
http://www.ebay.co.uk/itm/Audible-Flasher-Relay-Unit-Caterham-Westfield-Lotus-7-/221237441423?
