Driving through water triggers auto headlights?...

[crenca]

We don't get much rain down here (8-9 inches a year average) so I have always questioned myself, but today I confirmed it: When I drive through on road standing water of say > 1 inch that triggers a large push/spray into the air and back onto the hood/windshield (such that I turn my wiper's on for one or two wipes) my auto headlights are coming on about 10 or so seconds later.

This is happening in bright sun of the SW desert (I'm wearing sunglasses) so it's not a borderline situation where the on dash sensor is sensing low (or even low-ish) light. My low beams stay on for another 30 or 45 seconds after the splash event

Is this by design and if so how does it work? I don't have an exposed wire somewhere do I?

Sponsored

 

[Bigmoose]

The little red tinted bump in the center near the windshield is your ambient light sensor. You are getting enough on the windshield it seems to trigger the auto headlights.

 

[crenca]

The little red tinted bump in the center near the windshield is your ambient light sensor. You are getting enough on the windshield it seems to trigger the auto headlights.

I agree this is the most likely explanation...

However, the (granted dirty) water is on the windshield for a very short time as within about 2 seconds I have the wipers clearing it. Also, the ambient light inside the cabin/dash just is not changed that much. Also, I can take off my hat and place it over the ambient light sensor (I do this often, as I'm always putting my hats on the dash) and as long as I don't leave it over the sensor for > 10 seconds or so the auto HL's are never triggered. I'm certain the hat blocks significantly more light then these splash events.

Soooo, my experience is not adding up

 

[Bigmoose]

Do your lights trigger just by using the wipers?

 

[crenca]

Do your lights trigger just by using the wipers?

I thought of that explanation and tested that quite a bit today... And the answer is no unless I'm missing something.

 

[Brian_B]

I thought of that explanation and tested that quite a bit today... And the answer is no unless I'm missing something.

Auto lamps will come on with windshield wipers - usually after the second or third swipe. So not immediately if you are just hitting the sprayer or just washing away few drops from a puddle, but if you leave them on - yes.

 

[crenca]

Auto lamps will come on with windshield wipers - usually after the second or third swipe. So not immediately if you are just hitting the sprayer or just washing away few drops from a puddle, but if you leave them on - yes.

Okay, I'll have to more diligently test this and get back

 

[Valhalla]

And perhaps not in park\

 

[Sparkie]

We don't get much rain down here (8-9 inches a year average) so I have always questioned myself, but today I confirmed it: When I drive through on road standing water of say > 1 inch that triggers a large push/spray into the air and back onto the hood/windshield (such that I turn my wiper's on for one or two wipes) my auto headlights are coming on about 10 or so seconds later.

This is happening in bright sun of the SW desert (I'm wearing sunglasses) so it's not a borderline situation where the on dash sensor is sensing low (or even low-ish) light. My low beams stay on for another 30 or 45 seconds after the splash event

Is this by design and if so how does it work? I don't have an exposed wire somewhere do I?

Yes, by design.
Massachusetts and many US east coast states have laws that require your headlights to be ON if your wipers are on. Typically, my lights come on about 15 seconds after I start the wipers. This is a very convenient feature when I suddenly drive into a downpour (but probably not something Broncos living in the desert would experience). By the way, the lights always turn themselves off automatically about 10 to 20 seconds after the wipers are off.

 

[Smocaine]

Yes, by design.
Massachusetts and many US east coast states have laws that require your headlights to be ON if your wipers are on.

Texas is the same way so I'd be really angry if the autolamps DIDN'T come on with the wipers.

 

[Sparkie]

Texas is the same way so I'd be really angry if the autolamps DIDN'T come on with the wipers.

Yup, me too!
About 15 years ago, when I was teaching my oldest son how to drive, we were on a highway when we drove into one of those surprise summer sun showers. There was a light gray car about 500 feet ahead of us. I told him to watch carefully. The spray from the gray car and surrounding vehicles made that gray car nearly invisible. As he watched, he said "Whoa! It's almost gone." I replied, "The same is happening to you, so turn on your lights and slow down!" He knew why. A few years later, our state proposed the wiper/headlight law and he commented about that day.

Sponsored