There's two fuses for the Low Beam headlights in the underhood fuse box.

Fuse #1 is for the Left side low beam headlight.

Fuse #5 is for the Right side low beam headlight.

The way you can start narrowing down the problem is to grab a test light and check the test tabs on those 2 fuses for power when the low beams are turned ON but aren't working.

The way that circuit is wired is when the headlight switch is turned on, the Low Beam headlight relay gets energized and provides power to those 2 fuses.

So if you have power on those 2 fuses when the headlights are turned ON but the headlights aren't working, then it's a problem in the wiring between the underhood fuse box and the headlights.

But if you don't have power on those 2 fuses when the headlights are turned on but aren't working, then it's a problem with either the headlight switch (combination switch) or the Low Beam headlight relay.

What makes this harder to test is the headlight low beam and high beam relays are integrated in the Relay Control Module (non serviceable). 

If you look at the underhood fuse box, the Relay Control Module is in that square plastic box next to the headlight fuses.

To get into there you have to remove the fuse box and dismantle the entire thing. But there really isn't any point because you can't buy the relay control module separately from the underhood fuse box. It's sold as a single unit.

If you want to know what the Relay Control Module looks like in there, I found a picture of one. I'll put a red square around it. Notice that the row of fuses right next to it are part of it too. (in the picture the fuses have been removed as part of the dismantling procedure but you can see their terminals).

Like I said, if you aren't getting power on those fuses with the headlights ON it's either the combination switch or there's a problem with the Relay Control Module (or the connector going to it on the bottom of the fuse box).

I really don't think the problem would be the combination switch. It could be, and aftermarket switches are in the $40 range if you want to gamble.

It's more likely a problem with the Relay Control Module. Those underhood fuse boxes are really expensive if Honda even still sells them for that 2005 van.

You can find used ones on ebay for under $100. Just buy one from a good rated seller that offers a 30 day guarantee and free return shipping.

One more thing. Since this is an intermittent problem and if there's a cracked solder joint, sticking relay, or poor connection in that Relay Control Module, try giving it a smack right on the side of the part of the fuse box where that module lives. If the low beams come on, that will confirm you need to replace the fuse box. (That certainly isn't a definitive test to tell if the module is bad or not, it's more of an experiment just to see what happens)

check/swap headlight fuses/relays

My guess would be the light switch, check its output with a good OBD2 scanner - I think that on a 2005 chances are that the lights are controlled by the BCM.