should be 70 or 90 amp depending on the manufacturer date. you can check using the isuzu online parts site
www.myisuzuparts.com
but any seller is going to have applications data and specs.
just be aware not to buy a cheapo rebuild from the bigboxpartsstores. they almost univerisally don't last.
get a quality remanufactured unit from the dealer or from an independent parts store, my favorite are units remanuf by bosch. quality at a good (not cheap) price.
//bc