Windshield Wipers on my 97 work intermitently?

[fishmunger]

I was wondering if anyone else has had this problem? Seems like my wipers only work about 50% of the time. I have found that if you open the hood and bang on the black box that houses the circuit board, that sometimes makes them go. I presume it's an electrical problem...I'm wondering what I need to replace? The circuit board?

thanks for any ideas