wiring question, Old ibanez to squier

I have a 20th Anniversary Squier P/J Standard, love it because of the weight and the 1.5 inch nut, p/u's suck, even lousy paperweights.
I got pickups from a 83 Ibanez roadstar II. They have a brass plate on the bottom of each. The J p/u plate actually has a wire coming of it...is it a ground ?

 

thanks. It might have been an obvious answer to most, but what threw me odd was that there is no wire from the brass plates on the p pickup.