What year is your car? I am guessing that you have a car from the 70's which has had its dual chamber brake fluid reservoir replaced with a later single chamber type. I am not completely familiar with the float mechanism of the later type reservoir, but it should be very similar to the mechanism of the older style explained below.
The light you are seeing on the dash is a Low-Brake-Fluid warning. The way the warning light is activated is by a 'sinking float' mechanism. Inside the fluid chamber is a hollow plastic float which floats on the brake fluid. Attached to the top of the float is a (brass? bronze?) nail with a large flat head. The nail slides up and down in a sleeve as the float rises and falls: when the brake fluid chamber is full the nail rides high. The orange and black wires you see are the power and ground leads to the warning light circuit. Each terminates in a contact where you see them entering at the top of the brake fluid reservoir. Usually, the flat head of the nail floats above these contacts and the circuit is incomplete. However if the float sinks enough (usually because the brake fluid is low) the head of the nail moves downward until it comes to rest on the contacts, completing the circuit and lighting the light on your dash. You are thus warned of low brake fluid and impending loss of braking ability.
Sometimes the floats develop a leak, fill with fluid, and gradually sink, lighting the warning light even though the fluid level is fine. Sometimes, though, you have a leak in the brake system and you are about to lose your brakes, so check the problem carefully.
Now, the unconnected orange and black wire pair: the older fluid reservoirs had two chambers, (one for the front brakes and one for the rear) each with a float. The second set of wires should go to the second float. The later reservoirs are single chambered, with a single float, making the second set of wires unnecessary. It doesn't hurt anything to have them hanging there as your single float still activates (as it has) if the brake fluid level gets low.
Here's a picture of the earlier reservoir, shamelessly borrowed from Classic Alfa. You can see the hookup for the second set of wires.