Filter posts by custom fields

Hi,

Thanks for reading my question… ??

I’m building a site that uses Custom Posts and Custom Fields to show a vehicle inventory. I would like the visitor to be able to filter the posts by Custom Field or maybe by Taxonomy…

I already tried to make it work with the Query Multiple Taxonomies plugin. Works great but to prevent the dropdown list (i.e. Model) to become too long, I would like some dropdowns to be populated considering the first selection.

So when the visitor selects Manufacturer: Yamaha, the dropdown for Model should only show the Yamaha-models and not the Suzuki-models…;-)

I already did a lot of searching, car dealership, real estate, no luck so far. I can hardly believe I’m the only one looking for this.

Now I have 2 Custom Post Types: Motorcycles and Cars and a couple of Custom Fields to enter Manufacturer, Model, Color etc.
For my first attempt I also made some Taxonomies the don’t share at the moment.
If I have to, I can change that all but for now I don’t have a clue how to make this work… ??

Hope someone can point me in the right direction.
Thanks!

Kind regards,

Arne.