The attached is one board, a MOSFET driver, from an old power amplifier in our lab that unfortunately suffered a mini-fire recently. (Prior to its untoward warming, it operated from 160V rails and had a max current output of ~75A DC, with a O(100 kHz) bandwidth). The board design is from about 1990.
What is the 4-lead component in the green box? It's unlabelled, and as far as I can tell there is a negligible resistance across all four pins. It looks like two thick, plated wires joined by something chunky and wrapped in black insulation.
Am I being dumb? Is it just a jumper?