connector from mother board
were does connector at end of gray wire from mother board go
It may be that the wire that you are talking about is the WiFi antenna and it is connected at one end only.
Here’s a link to the ifixit iRulu AX760 Motherboard Replacement guide (you didn’t state what model iRulu tablet it is). In the image at Step.2 you can see the wire at the top of the picture, just resting on the insulated part of another connector.
Click on the link above rather than the image below to open the guide, scroll down to Step.2 and then click on the image a couple of times to enlarge it for better viewing
Just ensure that your WiFi is working OK in the tablet.