Have you checked the fuses inside the van and in the underhood fuse box with a meter? I have seen several fuses that have "looked" good, but were in fact bad.. they can actually break on the end, where the fusible link will look fine through the top, making them seem ok. _I would suggest using a test light on all fuses, a nad fuse will have power on one side, and nothing on the other.
If you have applied 12V to the parking light circuit and the parking lights turn on, then there is no physical damage to the circuit itself. It has to be a fuse, or the very unlikely possibility of the parking light relay going bad from being shorted out - this IS a possibility, but it is highly unlikely.
I have been in the Automotive Electronics business for 18 years, and everything is still telling me there has to be a fuse that was overlooked.Especially after you put voltage to the socket and the rest of the lights turned on.
The only other possible explanation for this would be the dashboard dimmer switch - I have seen on RARE occasions (and on GMC's mainly) when the dimmer gets shorted and burns up, the parking lights will no longer work due to the parking light circuit passing through the dimmer rather than just using it as a voltage source.