problems with putting up a ceiling light/fan

[euphonium]

hi could someone help please
i took down my dining room light and put up a new light/fan everything was working fine but the wire's from the ceiling (4 sets ) looked squashed but as it was getting dark i left it till this morning to try to sort it out
after taking the light back down and trying to get wires through the hole in the bracket for the light the wires that was twisted together i.e.
3 red wire's in a terminal block still in and connected
3 earth wire's still twisted together
but there was 3 black wires that was in a single wire and a double wire twisted together but they had all come untwisted to make 3 single wires
one was longer than the other 2 so i assumed that was the single wire
so i put that in the terminal block against the brown wire
the other 2 black wire's was the same length so i put them against the black in the block
then the earth wires went against the earth in the block i must admit the earth wire's i had trouble getting 3 in the block but i think i got them all in
turned the electric back on and the circuit breaker cut out
so i gathered that one of the black wire's was round the wrong way and changed it over
this time the light and the fan worked
so i put it all back together and checked it again and everything was fine
my problem started when it got dark
i turned the dining room light on from the switch in the living room and everything is fine
i then turned the kitchen light on and the dining room light went dim and the kitchen light was also dim
if you turn the turn the dining room light off and put the kitchen light on both the dining room and kitchen light's come on dim
so could anyone please tell me where i have gone wrong apart from touching it in the first place
i feel like a donkey but everything was working fine with the lights the light has been up for 7 days with all lights working fine but as it was my first day off work today i changed things around and now i have a problem
i can only assume i have one of those black wire's the wrong way round or maybe one of those earth wire's may not be in the connector block properly but i would like some advice before i start playing with it again
i don't want to make things worse
thanks

 

[PrenticeBoyofDerry]

You have mixed up your switch wire with the neutrals one of the black cables should have been marked up with red sleeve or tape.
Do you have multimeter or two probe voltage tester?

One of the blacks is not a neutral but a switch wire that comes live when the switch is closed (on position) the other two are neutral conductors.
The switch wire should be connected to the brown side (live) of the fitting and the two neutrals to the blue side (neutral) of the fitting.
If you do not want to mess about you need test equipment!

 

[euphonium]

no i have none of them
so does that mean if i try switching the black wires around till i find the right one things will be fine
or will i blow everything or kill myself trying

 

[PrenticeBoyofDerry]

no i have none of them

oh dear!

so does that mean if i try switching the black wires around till i find the right one things will be fine

no

or will i blow everything or kill myself trying

maybe!