Do i have a bad battery cable or bad fuse or circuit?

Everything in my car works fine but my heating/air conditioning and blinkers don't always work and they only work together. So if one doesn't work the other don't. Then i also have a bunch of corrosive build up on the negative clamp thing on my battery. I don't know if i have a bad battery cable or a fuse is bad or what. And after about a week my check engine light has come on. I need some help?