wjm, you are looking for the sophisticated connection, but it's the simple one in this case. Keyless entry means I use a remote to lock and unlock the doors - not the keys. Less wear and tear on the keys, less also then on the tumblers. All I need the keys for is the ignition lock.
The connection here is that for a keyless remote, you need a powered doorlock system you can wire into. Our bottom-end Honda I also did this to, and for that I had to install lock solenoids at all four doors - a real pain. By comparison, the 190E was a breeze, since that step was unnecessary.
'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7