The plug sits underneath the trailing coil, there are 5 black wires with red dots(I am asuming they are ground wires). They plug into a male fitting(green) that is bolted to the inner fender wall. In RED is the wire, BLUE: I know connects to two plug connector for the main relay.
p.s. If you cant see my picture please let me know.

Thanks

 

You should provide vehicle info.

If my guess it right, that is a picture of one of the main grounding points on an FC chassis. All wires are grounds.

 

O sorry I cant believe i forgot. here it is 1988 SE N/a and obviously an rx7. I have a bad ground from the wire in red, but I don't know where it leads.

 

Is is Tach signal(if that arrow is pointing to the yellow wire with the bullet connector).,.for the trailing coils.If you need to,you can plug a wire in and run a Big *** 10K aftermarket Tach!