S1000 not being seen by S100

[Seacom]

I'm trying to troubleshoot a system and I've not dealt with an S1000 before so am hoping you all here might have some insight.

The system has functioned in the past flawlessly for years, so I am to take from that the original wiring was all done correctly, it certainly looks clean and well done. The customer said he fried his S100, so bought a new one. He said he got the new S100 to register with his S1000 with help from Raymarine telephone support, but it never worked even that day. I however can't get it to register with it at all. I also can't get the S100 to talk at all with the S1000, it gets no bars of signal at all times.

I did not know to look for the inline power switch, but I did measure the power going into the S1000 and it read 12.1V (tho dipped to 11.7V by the time I finished troubleshooting attempts), so I take from that that it is likely set to On, or I would see no power at all, is that not correct?

I noted along the way that the C80 Classic was not getting a GPS lock the entire time I was there. I can see this causing operational issues with the pilot, but would this cause the 2 pieces not talk to each other at all? Not even to boot up or register?

Is there any tests that can be done to the S1000 itself to test if it's working period?