IT WORKED! I took the fixure apart, got the ballast specs from the
manufacturer's Web site, and then comparison shopped. I bought two
replacement ballasts at a local electrical supply, thinking that if one
ballast died, the other probably would too. The cost for the pair was
only $29 (versus $22 each on the manufacturer's Web site). I laid out
the wires as suggested, stripped the ends, then twisted, capped, and
secured them with electrician's tape. I reassembled the fixture, and
everything works fine. Thanks everyone for your advice!