said by Oedipus:
The 702G does not have wifi.
You are correct - which is why the OP would connect a Time Capsule via the Ethernet interface
and use the built-in Wi-Fi to supply wireless connectivity to other
devices in the home / office.....
TGRMTN - assuming the Time capsule is still set to get an IP address automatically, plugging it into the modem's Ethernet jack and re-booting it should allow it to connect with your modem. That would be the default configuration for the WAN side of the device. If that setting has been changed, either a reset - or network knowledge - will be required.