I have a Goodman furnace (gmpn080-4 Rev B). I want to install a new T-stat that is in need of a "c-wire". I have an extra wire in my bundle that is not being used that I could use.

I currently have a Honeywell that is only using 4 of the 5 wires, White (heat relay), Green (fan), Red (power) and Blue (cooling which connects to the screw labeled Y on the t-stat). All the rest match up to the correct color.

Here is my problem. I found on the internet a way to id the C-wire. Using a tester, touch the Red with each of the other three wires. If it jumps to 24V, then that is your C-wire. Since I am only using four wires right now, I did not expect to find one. The problem is, that I did. My white wire jumped to 24V when I touched it with the red wire.

So how do I wire my new t-stat if the white wire is both the heat relay and the C-wire? Can I split the wire and connect to both terminals (White and "C")?

Thanks for your help