Hi there everyone,
The truck has the switch with Auto, Off, Parking, Headlights, Foglights and dimmer control. Has worked great for years by just being on the Automatic setting. Unfortunately, now the switch must be manually operated because when on Auto, it ALWAYS blows the 25A fuse under the hood.
Is there a way to test the switch to see if it needs replacing or could this be a simple relay issue?

Looking Ford-ward to hearing from You!
TimmerDog

 

As you know whenever a fuse blows there is some reason for excessive current being drawn in that circuit.

Without actually checking the wiring and components with a meter , OR a thorough physical examination of associated wiring , it could be anything. Most times a wire carrying power to a component gets chaffed and now we have a short path to ground ,which is not right. It would be unusual for the switch to cause this , but not impossible.

 

It's not likely a switch or relay causing the fuse to blow. They likely would cause an open or inoperative circuit, not a short to ground. As mentioned, damaged wiring causing a short to ground or the lighting control module.

 

Thank you Hanky and Raski
Thanks for your input to my issue. This all began when we purchased our travel trailer and the dealer installed the brake control. That caused the wiring harness to fry a bit. They repaired the harness but that's when the auto light issue began. So we taped the word NO on a piece of masking tape and went back to manual switch use. I'll continue to tinker with it and hopefully, will be able to fix it.

Again my thanks to you,
TimmerDog

 

It always helps when ALL relevent information is listed in your post.If this all started with the trailor wiring addition (I am not going to call it an upgrade), I would take it back the the installing dealer to have the system checked.