I Put these cheapies on my 3. They work great.
http://www.jcwhitney.com/autoparts/ItemBrowse?storeId=10101&Pr=p_CATENTRY_ID%3A100000 217813&productId=100000217813&catalogId=10101&lang Id=-1&rlid=group_listing
You can also find the same type on Fleabay. I paid $14.95 plus shipping from an ebay sale.
On thing you should do is not wire them to the exsisting H3 wiring. The wire gauge is very small, 22 awg I think. The H3's horn is a low current horn. I chopped off the plug at the horn connector and wired in a relay in it's place to carry the higher current load.
Use a 14 awg wire from the battery in the horn power relay contact circuit to be safe.
Don't forget an in line fuse. I used a 20 Amp in line fuse and holder.
