Triumphrat

gm268

I think I've got it!

According to the manual the connection for an extra siren or pager output from the alarm has a "green and yellow tag". I'd read this and looked for it but it seems on second inspection that my closeup picture shows a miniscule amount of yellow back along the wire - this must be it, surely, even though I wouldn't describe the connection itself as having a green and yellow tag?

I can't for the life of me think what else it might be, and this would explain a zero reading on the meter (I didn't test it with the alarm sounding as I would probably be deaf by now). It also says in the manual that the position of the wires may vary, but that it should be recorded on the certificate of installation, so maybe not everyone's will be in the same place.