Er… their wiring seems correct? What are you checking it against?
I’m not the greatest expert on the Panzer IV but I do know a few things about it. Here is a box inside Miniart’s Ausf. J :

It’s the “Kasten 18”, the heart of the original intercom system, and it was eliminated from the Ausf. H. There is no way it should appear in an Ausf.J. This appears to be a mistake by Miniart.
That box was replaced by another switch box, the “Kasten 20”, and Miniart do provide it in their Ausf.J. Here it is :

But it’s in the wrong place. This is the Ausf.H position. For the Ausf.J it was moved up into the niche between the radio sets. This appears to be a mistake by Miniart.
Here, Miniart have placed the “Kasten 5” on the front of the turret legs, :

But in the Ausf.J, because of the deletion of the traverse motor, this box was moved to the rear of the turret legs. This appears to be a mistake by Miniart.
This is the hull roof. It should have two locking holes for the turret. They should be visible on the top side and underside. I’m showing you the underside, and one of the holes should be here :

There’s nothing at all in the kit. This is a mistake by Miniart.
Here’s a shocking one. The turret of the Ausf.J had a manual traverse. The traverse gearbox was much the same as any other version of the tank, except that the electric motor was removed. This is where it goes :

Miniart put nothing there ! Well, a tiny drive wheel, but nothing else. The gearbox should reach back to the gunner’s seat, it should have the handwheel and the firing trigger and the speed control… it’s big.

What are they thinking? How is the turret supposed to go around? This is Miniart being completely out of their depth !
Getting back to the Stug : I can’t see it properly, but as soon as I can, I will post an article about how to correct the intercom and radios, which I confidently expect to be wrong in several ways.
David