On the bottom of the Kyocera Yashica Z & ZL (and undoubtedly the Z2 & Z2L, and probably the X3.0 & X4.0) there is a small, oblong “tab” next to the tripod socket that covers up three electrical contacts.
I can find no information that these contacts are used by any accessory, so I ask, “What are they for?”
I think the truthful answer is that no one knows outside Kyocera's former R&D department.
It was provided for a dedicated accessory linked to the release terminal which is the three contacts to which you refer. That would suggest a remote switch of some sort though it would have had to have been supplied with a plate that screwed into the tripod socket, providing an offset tripod socket of its own, otherwise, when using the switch you could not mount the camera. I suspect it was never developed.
If there's no known accessory, they might be a set of diagnostic testing points or service contacts, if the electronics can be adjusted by sending signals from outside the body. Those would be more prevalent on electronic devices than cameras, but the service manuals or assembly guides might help to identify them. Does anyone have one or the other?
Most probably it is as lumiworx said, those are entry point contacts for service and diagnostic, checking the few pictures available on net of the X3.0 with transparent body looks like are part of the finder/film chamber assembly, also as shown in the following report (top right image):
From pages 7 & 8 in the Z/ZL instruction manual, it's the contact panel for a flash adapter. Adapter SM-S2 allows the connection of a flash via a standard flash shoe. The adapter attaches with a thumb screw that uses the tripod socket as the anchor point. It doesn't look like it has a passthrough for the tripod, so it seems to be for handheld use only. A pic of the adapter is on page 82.
It may well have been some sort of diagnostic access. Who knows? Do other cameras have similar electrical diagnostic contacts? I don't know of any.
My main reason for asking was to see if there were some other accessories for the camera -- one that needed electrical contacts. I don't know of any, but there was not very much that they could have added to the Z camera anyway. It's pretty complete, as is.
A member of the FLICKER Samurai Board asserted that it is a shutter release -- without any evidence. That could well be, because the camera lacked a remote release -- except for the built-in timed shutter release. I have my doubts about this suggestion only because the contacts are so close to the tripod socket. A camera being used with a cable or electronic remote release would undoubtedly be on a tripod -- which would cover up these contacts.