I've done this on several vehicles. I'd suggest adding an inline
circuit breaker (you can find them, along with solderable sockets,
at auto parts stores) and perhaps even a relay, whose coil is
energized by IGN or maybe ACC so that you are not adding
more current burden to the key switch - current would come
from B+ via the relay contacts instead. there have been some
makes*models that got recalled for ignition switch fires or melt
and who knows whether yours just got its recall buried?
You can find pigtailed cig lighter sockets / splitters at almost
any place that sells car care products, including Wal-Mart.