After my last post, yesterday evening, I went routing through the what-not (within the grotto) and extracted both the Mk 2 and the Mk 3 PCBs.
A quick look (with the aid of a magnifying glass) enables me to say that there is not a (duplicate) resistive-capacitive shunt across the pair. The "big yellow capacitor" just connects "terminal 3" to "terminal 2" (using the understood numbering as of the IDCs at an extension socket).
Interestingly I saw that the capacitor was marked "
1u8K250V". I can translate the "
1u8" to 1.8 micro-Farad and the "
250V" to be the maximum voltage rating but the mention of Kelvin (the upper case "
K" leaves me mystified. (Unless the "
K" indicates the capacitor type . . . it's not electrolytic, so polyester would be my guess.)