So 3 outlets, and an exterior light (bulb is fine) in my garage stopped working. These outlets (and light) have been working fine for years, this is a recent development. I already toggled the circuit breaker to no effect. The only thing that does work is the ceiling light. I drew a diagram, and i'm making an assumption of how the wire runs (i don't want to start punching holes). I'm guessing the problem is between the ceiling light (orange circle) and the ceiling outlet (red triangle). Can y'all suggest what i could do to diagnose what the problem is?
Your problem has all of the symptoms of a tripped or bad GFCI device. Insure that all GFCI's are reset. As far as diagnostics are concerned, at this point you will need a multimeter or ammmeter, or begin replacing parts helter skelter until you find or replace whatever is broken.
First kill all power to the devices and lights. Then you need to open up all of the receptacle and light fixtures so you can access their terminals. Then you can turn the circuit back on and using your meter, you measure voltage from your source to your neutral and ground. It should be reading around 120V. When you find the devices that are not reading 120V trace back to the nearest intersection where you are reading 120V and not reading 120V, and somewhere in there is where you have an open circuit.
I can say that before I started all of that, using my meter I would verify that there is 120V at the circuit breaker and then I would do everything I could to locate the GFCI.
If your house was built after 1978 then your garage receptacles will be required to be on a GFCI device.
Keep in mind you are looking at different subcircuits. The light presumably operates off a switched hot that works off a switch somewhere. The receptacles are (presumably) on an always-hot wire, presuming that the ceiling receptacle is for a garage door opener.
So if the cables are connected as you presume, then there is a /3 cable somewhere in there, or the light has a switch loop. It's also possible the two cable runs are not the same. No way to tell except start opening junction boxes and looking.
Do not disconnect things. The color coding is useless; the information about how things are supposed to go together is positional, eg. 1 white wire with several blacks. Tearing it apart destroys that info and greatly raises the difficulty of reconnect.