I am trying to install a new smart thermostat that requires a C connection. The previous thermostat used a 4 wire connection but there is a blue wire that's unused right behind the current thermostat. Problem is that I looked in the air handler and there are no terminals like most units, just a bunch of wiring. So trying to see if anyone may know where I have to connect the other end of that blue wire. Here are some pictures:
I am assuming the skinny blue wire at the bottom of the handler is the one routes to the thermostat but is not connected to anything. This blue wire is best visible in picture 1 and bottom of picture 3 (not the thick blue wire that has a white cap in the middle of picture 3).