How is the Speakon connector wired for REL sub?

@waterzlife I found the Neutrik NL4FX 4-Pole speakON Cable Connector to be superior to the Neutrik NL4FC 4-Pole speakON Cable Connector.
Although both will work the NL4FX has a more robust easier to use thumb mechanism. I have used both purchased on Amazon.
On Neutrik SpeakON:
Black 1-
Red   1+
Yellow 2+

Hi all,
I have a REL 328 with a Neutrik Speakon plug.
I'm connecting it to an Adcom A/B 535L 60w amp.
The amp has two R/L speaker terminals — "A" and "B"
Usually, I connect my main speakers to the "A" terminals.
I connect my REL to the "B" terminals.
I've watched the videos and have connected the REL Speakon plug (high-level input) to the REL and at the amplifier the Red wire to R+, the Yellow wire to L+, and the Black wire to L-

A couple questions.

1. HUM. I hear a bit of a hum from the REL when nothing is playing. A ground problem, no? Is there a way to connect it differently that will help with that?

2. TWO SETS OF MAINS + REL. If I wanted to connect two sets of main speakers simultaneously, would I just twist the REL wires in with the main speakers' wires at the terminal, still connecting as described above?

3. DANGER? Is (2) an inadvisable thing to do?

I see there's a lot of expertise here, and hope I've been clear. Thank you.

As I mentioned above your questions are answered here: https://rel.net/how-to-connect-my-rel/ find the session that talks about eliminating the hum.

2) Yes
3) No problem.

Try this to eliminate the hum, this should be in the video's I mentioned above, but maybe not.
Using the Neutrik Speakon plug connection as you stated that you are doing, now run a single RCA interconnect from the sub red line input to a red RCA input on your preamp. This should eliminate the hum.

Disregard my post directly above.
Three solutions to the hum problem:
https://rel.net/how-to-troubleshoot-and-solve-a-humming-issue/