I have a very old dimmer that I would like to replace as it doesn’t work. It is in the same box as another switch that controls a different light. The dimmer used to control a fan but we replaced the fan with only a light. The dimmer is the only switch that controls the new light. The dimmer only has two red wires. If it is a single pole why would there be two red wires? One red connects to a hot attached to the other switch in the box. If I buy a new single pole how should it be hooked up? Thanks