Here is a URL that gives many of the pinouts for the cables used by the modular access routers. Hopefully it includes the cables you are asking about.
If the serial interface shows up/down it is getting carrier but the protocol is down. If it has never been up I'd check with your carrier to ensure that the circuit is configured correctly and that your router configuration matches what the carrier has configured.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...