wrote:

Further to the issues I have been having with a broken SATA
data connector (which still works after being wedged on!)
I was wondering about the pin arrangement on the
connector. I note there are 2 transmit and 2 receive pins

Each pair is a balanced pair, like with a twisted pair in a cable.

with 3 ground pins...

My question is - what if one or more of the ground
pins were not connected, would the drive still work

Yes.

and if so is it dangerous?

Nope.

i.e. must ALL 7 pins be connected before the drive will work/be seen by XP?

The 4 data lines are crucial, not all the ground lines are.