Latitude 7390 touch screen not working

Hi, everyone, hope you're all well during these tough times.

I'm hoping someone may be able to give me some touch screen-related advice, albeit on a slightly unusual 7390 which I've put together from a mix of new and used parts from ebay, after I managed to get the motherboard for a very good price.

The mobo houses an 8350 CPU, and originally came mated with a touch screen display. I managed to get the original display from the same seller, but the courier trashed it, so I had to buy an original Dell replacement touch screen assembly (lid, bezel, screen, etc) to replace it. Post-trashing, the original TS partially worked when connected to the mobo, but the screen was too cracked to use otherwise.

I've got the small touch screen connector of the new screen assembly connected to the relevant connector on the mobo, but while everything else on FrankenLatitude now works, I'm not getting anywhere with the TS.

In the BIOS, with the original screen connected, there was a notice that mentioned the screen's touch capability, IRRC. There's no such notice now. I can't find any specific TS drivers on the internet, though there's a list of devices in Device Manager under Human Interface Devices, and I'm wondering if some of those might relate to a TS:

I've got the serial IO driver, and the HID event filter drivers installed, so I'm just wondering if the HID entries above might suggest the TS is physically recognised by the mobo but needs drivers, or if those HID entries relate to some other hardware. I don't remember the TS connector being keyed, so maybe I just got that connector the wrong way up when I connected it to the mobo... Plus, I haven't updated the BIOS since installing the new screen (BIOS is currently 1.1.6, IIRC).

Any input much appreciated (apologies for the pun)

Many thanks, Jon.