Hi There.
It sounds like I bought the same payware item for 2010. With that edition the wipers are suppose to switch on automatically when it rains and then switch off automatically when the rain stops. I would think it was the same for Trainz 2009.
However, I found that the wipers where continuously on whatever the weather and the only solution I could find was to clone the asset, rename it and then delete the wipers from within the config file of the clone.
I now have two versions of the 170, one with wipers and one without. It is not a perfect solution but it does look a bit more realistic in dry weather.
I do not think the problem lies with the asset creature, it's almost certainly a problem in the Trainz software programming.
Hope this helps
Bill