Jim, While it will certainly work, you do not need a bridge rectifier for your application. Two of any silicon diode that is rated for at least the load of your beeper will work. Say your buzzer needs 250ma, (1/4 amp) A # 1N4007 replacement will work for anything up to one amp so it will be plenty. Extra current capability is no issue, so 3 or 5 amp rated diodes will work fine also. It is pretty hard to find a silicon diode rated for less than 50 vdc so you do not have to worry about serving a 12 volt system. the auto parts store can also be a source. The "trio diode" for any 1970's to 1990's GM alternator will wok also. (not to be confused with the "rectifier pack") The side that has one leg hook up to the beeper, the side that has three legs hook one turn signal power lead to one of them, hook the other turnsignal lead to another leg, and tape off the third. the Anode/cathode polarity is already worked out for you.
To simply use two silicon diodes, connect the end with the stripe (cathode) of both diodes to the same terminal on you beeper. The other terminal of your beeper goes to ground. Connect the anode (no stripe) of one diode to the left front turn signal power and the anode of the other to the right front turn signal power. Any time a signal light is lit, your beeper will chirp. Good Luck
