How do you replace a bulb in the White Knight back up lights ?

I have a 02 S-10 pickup with the permanent mount backlights by White Knight. These are the ones that stay on the trailer hitch even when the hitch is in use.
You just pry off the little plastic cover over the hitch tube when you want to use the hitch. They have a three position switch on the back of the unit.
I need to know to change a bad bulb in this product. Where can I get instructions on this unit?