The taillights and running lights are not working?

The reason you've seen the headlight switch as the fix is because normally it does solve the problem. Those that don't are the ones that show up in the forums you might be seeing. One thing to check that I've seen more than once is a trailer wiring harness that is chewed up next to the ball. If you have a trailer harness inside the van, or inside the trunk on cars, check if something got placed on top of it and the wires rubbed through. We also used to run into shorted trailer connectors installed by U-Haul back in the late '90s. They had three red LEDs to show when the taillight, left signal, and right signal were activated. Those connectors developed shorts that would blow multiple fuses.

Due to the cost, you might consider harvesting a used switch from a salvage yard. If you do, look closely at the terminals. If you see any black or charring around any, typically two of them, look for a different switch. That overheating can develop between a pair of switch contacts or between a terminal on the switch and its mate in the plug. Either way, that heat will migrate into the other part, so the only proper repair is to replace the switch, and to cut out the terminals and replace them, along with about four inches of wire.

The next thing to consider is a trick that allows you to power up the circuit so it can be diagnosed without blowing a lot of fuses. That is to use a small light bulb in place of the fuse. When the circuit is powered up and the short is present, that bulb will be full brightness and it will limit current to a safe value. I like to use a common 3157 brake light bulb. Those limit current to one amp. It will get very hot too, so watch that it's not touching anything. Now you can unplug things and move wire harnesses around to see what makes the short go away. When the short is gone, the bulb will go out or get dim. In this case it will only dim a little because it will be "dropping" most of the 12 volts while all the running lights will share what little remains. If you use a larger 9004 headlight bulb, it will dim more when the short is gone, and you'll likely be able to see the faint glow in the taillights.

These drawings show a simplified version of what I'm trying to describe. See how far you get with these ideas, then let me know how you'd like to proceed.

Hi,

I noticed it has been a couple of days since we heard from you. Have you been able to make any progress? We are interested in knowing.

Take care,

Joe

Dandy news. Are you saying it needed a switch and a fuse? Very happy to hear you solved this. Please come back to see us with your next conundrum.

Thank you. Please come back to see us again.