Need help with basic electrical stuff

Hi all,

My amplifier has an error and I've talked to the designer. I'm told to "Check the DC voltage at the speaker output related to GND (e.g. XLR Pin1)

I'm unsure of what to do.

1)Where do I put the black and red cable from the volt meter onto the amplifier,

2) and should the amp be on.

3) What do I do regarding the XLR Pin1

Appreciate any help I can get, thanks all.