Help me ID a connection

I’ve had this Todd PC-30 power supply to run radios for a long time. I’ve never been able to ID the purpose for the connection in between the ground and The + - power connect. The black one with the screws. It’s connected to a blue wire but doesn’t register on my meter. Anyone have an idea?

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It reminds me of the old antenna connection for our TVs back in the 70s.

Without really tracing where it goes on a schematic of the supply, it’s difficult to tell what exactly it is for.

Standard terminal block though. The left piece is called a bridge and is meant to hop over the plastic isolator to keep the two circuits separated and tie them together.

I appreciate you taking a look and trying to help me out. I’m going to try and get a picture of where the connections wires go. It’s tough cause I drilled out all the rivets and then bolted it back together. Definitely don’t want to pull it apart again… It produces 13.94VDC and doesn’t budge any, it’s a good clean power without any noise. It appears that one wire goes to behind the coils and the other terminates just below where the ground does. These pics may help some. Otherwise I’m gonna forget em and drive on with banging out some CW. image image
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If you are able to zoom in tight, you’ll see a clearer view of the navy blue wires with a white stripe. It seems to follow a path that I’d associate with a ground? Electronics aren’t my strong suite so anyone chime in. I’m not the kind to try and sharpshoot. Just want answers. I’m going to try and get a wiring diagram. Anyone else have history with these devices? It’s really clean power, great for HF/CW.