bathroom fan and built in light

[marksmachines]

i am refitting my bathroom and have fitted a over head shower fan with built in light, the problem is on wiring it up it will not work unless i disconect the 12 volt transformer for the light and then the fan will work not the light.as soon as i connect the transformer for the light nothing works , any ideas please

 

[ban-all-sheds]

Either the unit is faulty, or your wiring is faulty - it's impossible to tell from your description.

If you live in England or Wales, what are your plans regarding notification of this work? The simplest and cheapest option might be to have an electrician install the light.