filter multiple attribute values PS 1.7

[wiros]

I want to be able to filter my products with 2 or more options on each group (PS 1.7.2).  we have a group called ' Voltage' which give the possibility to filter products that are suitable for different voltage levels. Universal products can be used on 12 or 24 voltage, but the filter menu will only let me select 1 option.

Does anyone now how to make this setting of what module we need for this?

[selectshop.at]

Than you configured the filter wrongly. You need to add to the group both characteristics. Check the configuration of your filter module. It is possible to have more than one characteristics filtered per group.