Replacing sensor for light switch

[Darling]

Help!! In the hallway of my flat, someone fitted an outdoor sensor that operates the hall light when you enter to room. Obviously I want to change this for a normal light switch.
I disconnected the sensor that was fed with 2 x 3 core cables both with 1 x red wire, 1 x black and an earth.
The sensor was wired up with 2 live, so the 2 red wires went to these, then the 2 black wires connected with 2 blue neutral terminals and the earth wires were twisted together and to one side.

I then wired a light switch as follows,

2 x red wires in COM terminal
2 x black wires in L1

When we put the power back on the light worked but the switch was in OFF position. When we switched it to ON the fuse tripped.

We haven't been able to get it working since!. We were advised that no neutral is needed ( we are thinking the black wires are neutral due to how they were wired into the sensor ) in a light switch. So we rewired the live feed red wire into COM and the red Switch wire into L1. Isolated the 2 black wires seperately and put the earths as should be in the back of switch box.

Any suggestions as to why the light doesn't work? Could one of the black wires actually be a live wire?

Any help gratefully received. Many thanks

 

[Spark123]

The blacks sound like they are neutrals - they need to connect together in a piece of terminal block - they do not connect to the switch.
Both the earth go together and to the back box (link to the front plate if the switch is metal)
One red goes to Com
The other red goes to L1

 

[Darling]

Many thanks for your quick response. I've just tried as you suggest but although the light now works, the switch doesn't turn it off? It just stays on permanently no matter which way I flick the switch?

When I did it wrong earlier, could I have made the switch faulty? Can anything "blow" in a switch?

 

[Spark123]

Yep - by putting a short across the switch it is possible to weld the contacts together so it is probably new switch time.

 

[Darling]

I reckon you're right. Will get myself a new switch tomorrow.

Thanks again!