Do i have to pre-lighten my dyed black hair??

My mousy brown hair is dyed black at the moment, last dyed 3 months ago. I'd like to dye my hair a vibrant red colour. Would I get a better result if I prelighten it first before dying in the red clolour??

Yes, if you lighten it first you will get a more vibrant result. If you only want a subtle hint of red then you wouldn't ned to lighten it. Keep in mind that red dye fades the fastest out of all the colours, so you need to use shampoos and conditioners that are specially formulated for red coloured hair (it should say this on the bottle).

yes
nothing shows through black
black is the darkest colour there is
the only dye that shows over that is more black
so if you want any lighter colour than black, you have to lighten it
and this is usually only done by bleaching
with ruins your hairs health, strength and shine so its best to get this done profesionally at a salon

You could get a few pieces of your hair highlighted (like streaks) and then put the red dye on your hair and it will show up brighter on the highlighted bits. I've done this before, it can look cool if that's the look you want.