If your new spotlight is a low voltage jobby then you'll need a new low voltage switch. Standard dimmer switches won't work with low voltage spots because the dimmer is only lowering the input voltage to the transformer (which isn't good practice at all!) not to the transformer's output, which is what you want.
question for cobweb, what do you suppose happens if you use an electronic dimable transformer?
A) the input voltage gets reduced
you are right in respect of an ordainairy transformer and you can not use a dimmer with this, however as it is a light with 3 x 40 watt lights, i have not heard of a 40watt low voltage lamp, 20w 50 w and higher but not 40.
I would therfore assume that the new light has 3 x 40 mains lamps, and it has been connected wrong (it is easily done)
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local