Help! - how to test an SLM-C?

I have a second-hand SLM-C and second-hand CDL-3.
The bits came with a short loom - with this set-up I couldn't make the make SLM-C do anything.
I bought a new track kit loom, complete with plug for SLM-C.
Still can't make the SLM-C show any signs of life.
I checked continuity between SLM-C plug and wiring inside rear of SLM-C - all fine.
All dash function work fine, have latest firmware.
How can I tell that the CDL-3 has even found the SLM-C?
Can I diagnose a CAN problem with the SLM-C?
Do I need to add a resistor, given that the new loom is meant to have the SLM-C plugged into it? (Total distance between dash and SLM-C is about 30cm.)
The bits came with a short loom - with this set-up I couldn't make the make SLM-C do anything.
I bought a new track kit loom, complete with plug for SLM-C.
Still can't make the SLM-C show any signs of life.
I checked continuity between SLM-C plug and wiring inside rear of SLM-C - all fine.
All dash function work fine, have latest firmware.
How can I tell that the CDL-3 has even found the SLM-C?
Can I diagnose a CAN problem with the SLM-C?
Do I need to add a resistor, given that the new loom is meant to have the SLM-C plugged into it? (Total distance between dash and SLM-C is about 30cm.)