Insulation advice needed

[jsouthco]

While replacing my Water heater yesterday I noticed quite a draft coming through between the foundation and the Joist that runs paralell to it. The opening between the 2 in only a few inches wide and the area behind the joist is full of wires running out of the main fuse box.

Any ideas on how to address the area and eliminate the draft? The outside of this wall is under a low deck and I cant get to it now to do anything from this side.