Lights come on when driving with switch on off

[Auto owner]

When I’m driving above a certain speed (being about 5mph) my headlights will come on even with the switch on off or auto. I can turn them off again by turning the switch onto “on” then “off” again. If I turn them off and go slow they won’t come on. But as soon as I go above ~5mph they come on. They will stay on even with ignition off and key out, but if I turn the switch to “on” then “off” and turn the ignition off, they won’t come on. This came after an issue I had where I couldn’t even get them to go off which was due to water ingress going into/onto passenger side fuse box. My relay seems fine, my Battery connection seems fine, no more water in my car/coming in, and my switch does work as intended when under ~5mph. Any help would be massive. Thank you

[Herbie]

Do they come on properly, i.e. full brightness, or are they dimmer than usual?

I'm thinking there could be a backfeed from some other circuit due to the water ingress/dampness, or current tracking across the passenger side fuse box. How did you dry it out and are you sure it's completely dry? Did you use anything like switch and contact cleaner to clean up where it got wet and have you checked any earthing points for cleanliness and tightness around the area?

[Auto owner]

2 hours ago, Herbie said:

Do they come on properly, i.e. full brightness, or are they dimmer than usual?

I'm thinking there could be a backfeed from some other circuit due to the water ingress/dampness, or current tracking across the passenger side fuse box. How did you dry it out and are you sure it's completely dry? Did you use anything like switch and contact cleaner to clean up where it got wet and have you checked any earthing points for cleanliness and tightness around the area?

They are not dimmer at all. Standard brightness. And I used one of those moisture vacuums to suck all the moisture out of the car, also before hand drying out the underlay/carpet/mats myself with the power of the sun over the course of a couple weeks. I have also taken out the passenger side fuse box and dried it as that’s where the previous water leak was. People from my work also believe that could be the case with a back feed.

[steve2006]

Do you have factory fitted DRLs or not?

[Auto owner]

11 hours ago, steve2006 said:

Do you have factory fitted DRLs or not?

No it doesn’t have DRLs

[steve2006]

With no DRLs fitted the headlight wiring is pretty simple with a fuse for each side, a relay and the headlight switch.

There is no direct connection to the speed of the vehicle.

I would thoroughly recheck the fuse panel for corrosion resulting from the water ingress and the headlight relay to ensure it is opening and closing correctly and not sticking closed.