Gauges and electrical gremlins

I was trying to help a buddy out today with his car. He has gauges that will peg (jump to full) whenever you turn the ignition on. After digging around the dash and finding all kinds of historical $%^kery we still have a few issues. Two gauges still "peg out" when powered. But, this thing has really got my head scratching. After looking around and tracing lines, etc we found this on the firewall pass side of the car. It has positive feed coming from battery and a bunch of other powered things on the far right terminal. We are tracing whats on the 2 terminal (left right as you face it) but there's another large feed wire on the first post that appears to go down to starter.

That said, powered on or not I can only get reads on the 4th post (the one with all kinds of leads attached). It is constant power. The other 3 don't seem to do anything...

Can anyone tell me what the heck this thing is???wtf.jpg