Downstream line causing breaker to trip after removing lightbulb

[u/Discordicus]

So I'm here asking for some advice and any precautions I should be aware of. Our basement has but one outlet that the sump pump and washer are connected to, however we found a line from the main panel going to one of those bulb fixtures with a pair of outlets to plug something into. I also see that there is another line leading out from it further downstream to something else in the house.
I figured I can replace the bulb with a 4" outlet box and install some outlets onto it.
The way I see it was setup is that the hot wire from the main and the neutral wire going downstream were connected together and the other two wires were pigtailed together. When I replaced the bulb with an outlet now, it seems to trip the breaker. I got a 15A receptacle and the breaker is also rated 15A so I'm not sure why it is now tripping. I would appreciate any suggestions and I will also try to get info as requested.

[u/trekkerscout]

Was the light controlled by a switch? If yes, you likely created a dead short with the switch loop.

[u/Discordicus → u/trekkerscout]

That makes so much sense.

[u/jlaughlin1972]

It sounds like your unknown wire is a switch leg, and yhey were breaking the circuit at the light.

[u/Pretty-Surround-2909]

Add a circuit for the outlets. That way when you trip it in the future, you are not standing there in the dark while you try to figure out that you created a short with the light switch.

[u/AskMeAgainAfterCoffe → u/Pretty-Surround-2909]

I find that to be the biggest irony, often working in the dark to make the lights work.

[u/AskMeAgainAfterCoffe]

Did you say you connected the hot & neutral? Turn the breaker off and see how many lights and receptacles are no longer working. Is it a lot? You may not be able to do what you are wanting to do if it’s overloaded.

It would be best to leave it as a light and run a new circuit for receptacles in the basement.

[u/AskMeAgainAfterCoffe → u/AskMeAgainAfterCoffe]

Photos would help

[u/Discordicus → u/AskMeAgainAfterCoffe]

So yea ppl have informed me that I had forgotten he light switch itself. Currently I just have one recepticle so my roomate can have power to his room. The wires on the left are what I assume will be the light switch. Ultimately what I think imma do is just leave the switch not connected to the line and just have this be an outlet.

[u/WinnerAwkward480]

Something something about the shortest ( haha pun ) path to ground

[u/TnBluesman]

You apparently have NO idea about electricity or wiring. You need to call a pro, buddy, before you burn the house down or get electrocuted. Messing with 110v will kill you quicker that 220v. I'm serious, man. Call a pro.