Its called a "shunt" , its a resister to parallel the internal resistor of the coil. it helps provide a steady gauge that doesnt fluctuate with every little voltage change. It should only go on one way it goes across the two terminals for the gauge. i believe it is horizontal.
Thanks for posting! That's how I put it back in (horizontal) and I just wanted to make sure I had it right before I put it in the car later this coming week!
