Oh dear that ages me.
In 1980's I did some casual work for a fitted wardrobe manufacturer/installer who specialised in housing developements and of course all of the SE fitters did kitchens too so there was regular multi room cooperation (as in: wire this for me while I fit and align some of your doors).
I have fitted several sets of these, correction fitted one set and wired a dozen or so, the hotplates were supplied with a terminated heat resistant flex and a couple of (very specific) cable clips, the controls were 2 different makes or styles:
One style had a matching plate requiring a big cutout, containing the control knobs and a set of terminals for each cable (hot plates, supply and possibly cooker hood and oven) ,
The other had individual control units which could be mounted anywhere, these were commonly mounted to a plate under the worktop (which I imagine it the case with this one) so just the knobs shew but the option was to dot them around nearer each hotplate.
Generally the hotplates were set in a straight line nearer the back of the worktop which I always thought was wrong as the housewife would be constantly leaning forwards (before any sexist comments I only mentioned housewife as they tend to be shorter and therfore a more acute leaning over angle)but it did retain almost half of the worktop for other use.
There was/is a neon on each hotplate which could be wired to show it was either: Switched on, heating, not heating.
Oh dear far too much nostalgia