I'm having trouble locating a service manual for your vehicle, so lets attack this the same way I would any other one. Grab a test light and remove any covers that prevent you from taking readings on the connector of the head light switch. Back-probe each wire one at a time. You should find at least one that has voltage all the time. Write down that wire color and mark it "12 volt feed". If you find two or more, list them the same way.
Next, put the switch to the running light position, then test all the wires again. You should find one with 12 volts now that didn't have it before. You might find two, and there might be one with less than 12 volts. That would be for the dash lights. Write those colors down and label them.
For the remaining wires, put the switch in the head light position, then look for wires with 12 volts that haven't had any voltage up to this point. You should find one wire with 12 volts, then a different wire with 12 volts when you flip the hi / low switch.
If you make it this far, with two head light wires with voltage, the cause of the problem is after the switch. The most common suspect would be where the wires go through a plug on the firewall, but to have two corroded or broken would be quite the coincidence. I'd sooner expect to find that plug is not pushed together all the way.
If you didn't make it this far, I just remembered there should be two 12 volt feed wires, one for the head lights, and one for the flash-to-pass system. If you only find one wire with 12 volts, pull out that circuit breaker again, then retest the wire. If the 12 volts is gone now, that's the 12 volt feed for the flash-to-pass circuit. We would need to figure out which wire is for the head lights, and why the 12 volts isn't getting there.
I also see that you implied the head lights AND the running lights didn't work originally, but the running lights do work with the new switch. Your old one may have been defective, and the new one could be for a different year or optional system, and it could be wrong for your vehicle. Also, if you're missing a second 12 volt feed wire, the fuse for that is most likely under the hood, not inside the van. That fuse is almost certainly going to be different than the one for the flash-to-pass circuit.
Sunday, August 31st, 2014 AT 7:43 PM