I figured it out thanks to Richters ' wiring simplified' and by studying the current situation deeper.

However, I wonder if this is a bad setup??

Furnace (gas) is on a 15 amp circuit with 14AWG. The power goes into this pullchain fixture before going into furnace switch box.

Is it a bad idea or against code that the pullchain light serves as the junction box before the furnace?

I figure that circuit should just be dedicated to the furnace (fan) which is why I started tinkering. A previous owner had ran 12/2 from that same junction box to some undercabinet lighting as well. They had doubled up on the screws to the light fixture. I removed the 12/2 line and only have the pullchain lamp junction on the furnace circuit as described above.

Source is spliced in the middle of the wire (not snipped at end) and looped around fixture screws then piggyback/nutted to the furnace.