I have an odd issue... hence why I'm here! I am replacing an old ceiling fan with a standard light fixture. The house was built in 77, so there is a bundle of wires up in the ceiling j-box with one 2-wire run to the switch. After removing the fan, I have NO hot wire in the switch box. tying the third black wire to the load bundle in the ceiling pops the breaker when the switch is hit. I'm hoping one of you can help provide some clarity for me on how to wire up a simple light fixture to this complexity of wiring.
I think the problem is that you have the white wire which is the return of the switch leg tied into the neutrals. This creates a direct short when the switch is thrown.
Find the white that's in the cable for the switch loop, mark it with black tape (because it's technically a hot), and use it as the hot for your fan. Connect the fan's neutral wire to the white bundle. Then you can put all black wires together.
The third black wire is probably an outgoing branch for another light or outlets. I think this is your scenario (you can reverse black and white in the switch loop if you label the white with tape):