New Thermostat with 'c wire' hookup
I have a Goodman GMPN100-4 REV B, and am attempting to hookup a new 3m Filtrete Thermostat with WIFI from Home Depot. It takes batteries but it also requires a 'c wire' hookup for the WIFI to operate. I have removed the stock Honeywell 4 wire thermostat with R, Y, W, G hookups. There are unused wires that run from the thermostat to the furnace that I can use for the 'c wire' connection. It is my understanding that the 'c wire' hookup is for 24v power.
My question is: Where do I hook up for the 'c wire' connection on the circuit board ? Within the furnace I have an open place labeled '24V HUM', which is unused. There is also some sort of transfomer with multiple wires connected labeled 24 on the lower and 120 on the upper with multiple red, blue, and white wires leading out. Can I attach to either one or am I totally wrong?
Any help would be appreciated and I will respond to any questions, if any.