Panasonic KX-TC1743B Service Manual page 40

(*1) See Base Unit Reference Drawing () - Should return to OPEN after entering the Test mode.
(*2) While the Tele line is connected, the "Caller ID" LED is ON/OFF as well.
(*3) It shows whether the telephone line is connected or not.
-ON: OFF HOOK.
-OFF: ON HOOK
9.2. TAM Test mode flow chart
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