Gti to diesel glow plug relay

Howdy folks, Ihave a glow plug relay in slot 2 on my fuse box originally for fuel pump relay. I have the glow plug  wire with the big fuse plugged into the back of the fuse box yellow plug in picture. The slot is a bit damaged where relay goes . . So my problem is the glow plugs heat up sometimes (they're new)As is the relay . Am I missing something with the wiring or could it be down to the damaged slot? Many thanks