Briggs alternators vary in output from 1 amp up to about 15 amps, depending on alternator model. The diode has to be rated for at least the alternator's rated current output. Mechanical design is also important - a 15 amp diode will have to dissipate 10 Watts at maximum current, which requires that it be bolted to a decent heat sink. So, first you have to find out the alternator's current output, and look at the mechanical design of the existing diode. If it is only a 1 amp alternator, chances are the diode will just be a tiny black cylinder incorporated in the output wire and will dissipate heat through the connecting wires - it will not be bolted down. See why pictures are needed to resolve any of this?
