One more question, please. I took the fixture out and put the outlet in where one light was. The ground wire was rolled up inside the housing for the light, unconnected, so I connected it to the outlet. Tested it and it worked fine.
The second light must be connected in line to the first light. The ground wire is rolled up in the housing again and not connected though I cannot tell if it was cut anywhere. The black and white wires are connected with wire nuts in the housing. You may be able to see this in the pictures. A black and white wire ware then connected to the old light fixture with no ground wire. I didn't do anything with this one yet. Can I just connect the black and white wires to the outlet or do I need to do something with the ground wire? Thanks for any advice.
As Jim111 indicated, to be code compliant, these should be GFCI protected.
Keep in mind if you are under NEC 2014 code cycle, any receptacle outlet in garage must be GFCI protected
You can accomplish that in a couple of ways. Each outlet can be a GFCI, in which case you would simply connect the white, black, and Ground wires to a GFCI outlet's line terminals at each fixture. Another way is to identify which fixture power is coming from and disconnect the bundles of wires wire-nutted together and connect the wires providing power to the line side and the wires feeding the second fixture to the load side (typically the load side terminals have a label covering them that have to be removed). Once this is done, the second fixture would replaced with a normal outlet. It looks like that box has three wires in it. So, identifying which wire goes where might be difficult.
If you aren't going to install GFCI for whatever reason (which I don't recommend) and you are going to install standard outlets, you still need to connect the ground wire on that second fixture. The easiest way to accomplish this, in my opinion, would be to use the white and black pigtails that were attached to the lamp and attach them to the outlet. Then you will need to come up with a short piece of equivalent sized bare ground wire to make a ground pigtail that would connect from the outlet to the ground wires wire-nutted together in the box.
I don't like GFCI outlets on the ceiling for obvious reasons. I have ceiling outlets in my garage for a few things like my lift and the garage door opener light. I installed GFCI outlets on the wall to feed these so that I can reset them without a ladder. But I was installing new circuits when I did it and had the access. Another, albeit more expensive, solution is to install normal outlets in the fixtures and replace the breaker for that circuit with a GFCI breaker.
It's hard to tell much about the box size from those pictures, but you also have to make sure that the box is rated to hold the number of wires it has along with the outlet you are going to add. You might need a box extension to avoid exceeding the box capacity.
