In the bathroom I have two lights and two switches that are all wired together. Each switch can turn on/off both lights. I am replacing these lights with canister lights. My problem is when rewiring the light, I can not get the new light to turn on/off. One side has a red, white, black, green. The other side has white, black, green. The light has white, black. The house is 30 years old. I think the red is the switch but I don't know how to rewire this light. Please help. I have tried the other light yet.
Sounds like when you say "one side" you are talking about the light boxes not the switches. If that is the case? the box with the most wires in it probably has 2 blacks together, 3 whites together, all greens together, and a black and red together, If this is the case then the black and red should connect to the fixture black. The white from the fixture goes to the other 3 whites.
The other box is easy black to black white to white throw the switch and see the light. :-)