Headlights Staying On

Wife noticed this morning@ 4AM the headlights were on (2001 Tundra). Tail lights were not on. I went out and the headlight switch was OFF. I started the truck and the headlights went OFF.

Strange...

I moved the truck to my garage, turned it off and the headlights went back on again, so I disconnected the battery. We had rain last night and the truck was outside. Don't know at this point if it is a corrosion issue due to the wetness or a hardware issue.

Anybody got any ideas or can someone post up the wiring diagram for the headlights?

 

There was a thread with a very similar issue a year or so back.

Here is @BubbaW's quote with the field service manual on it. It should be able to help you more than I could.

 

Thanks. I'll have a look...

 

No resolution in this thread, but here's a link anyway.
https://www.tundras.com/threads/running-lights-and-dash-panel-light-problem-help.77545/

 

Yes. I haven't found much about this problem. On another forum someone mentioned replacing the headlight switch assembly...

 

That's not a cheap part, but if you could get one from a junkyard that'd be the cheapest route for testing.

 

Wonder if there is a switch test on the FSM.

 

I would suspect the headlight relay of sticking. The vibration of starting the truck was likely enough to release the relay.

 

There's an auto-off circuit too:

 

Swapped out the headlight relay with the fog light relay. No change. Disconnected the battery for a few hours and reconnected. Headlights came back on after a few minutes of reconnecting the battery.

We had rain last night so I'm wondering if the integration relay got wet. I've heard of leaks in the windshield causing problems in that area. So, I guess I'm going to inspect that area to see what I can find.

While I had the headlight relay out I checked the terminals with a multimeter and found 12vdc on the two pins that energize the relay. Obviously, that is not supposed to be there when the vehicle is shut off. I guess what I need to do is pull the relay again and then start the engine and see if the 12vdc goes away, because when the engine is started the headlights do not illuminate.

When pulling the relay, I noticed that it caused the headlights to go out. So the results of this test was expected...

More to come.

 

Interesting problem. I'm guessing it's your driving light function that is stuck on. You can disable the driving light feature. There is a plug that's located between the battery and firewall that you can disconnect to achieve this. I've disabled my driving light feature because I'm the decider.
2020-11-19_08-54-09 by GhostCreekMine, on Flickr

 

Thanks Glock. I don't believe my 2001 has automatic headlights (DRL), so I cannot implement your fix...

Oh, one more data point.... sometimes my horn doesn't work. Wondering if this is also tied into the integration relay...??

 

I had the same issue, traced it back to the wiring harness where it enters the fuse box in the engine compartment. The insulation had degraded on a couple of the wires and it caused my headlights to randomly come on.

 

The horn works off of a relay too. How are your blinkers? Everything ok?

 

I'd still try disconnecting the plug I pictured as a test... just to see if it effects anything for you.

 

Update...

If you can call it that as nothing really definitive has been done other than me disconnecting the battery and attempting to remove the integration relay under the dash. I removed the lower dash panel but quickly saw that it was going to be difficult to disconnect all the connectors and remove the box. Additionally, it appears that you will have to remove some of the HVAC venting to be able to get to the bolts holding the box in place. I did remove one of the connectors from the front of the integration relay and felt around the back with my hand for any signs of moisture.

Found nothing.

So, this morning I plugged the connector back in and hooked up the battery. The headlights did not come back on. After and hour or so I re-installed the lower dash panel. Its been several hours now and the headlights haven't come back on. I drove the truck into town for lunch and came back and all seems to be good - for the moment. I don't think anything is fixed at this point, but I can't replicate the problem at the moment.

So, until this issue rears its ugly head again, I'll have to take a pause for now...

 

Hoping the Hand Mojo did a fix. Sometimes thats all it takes.

 

Jiggle the handle. Fixed a lot of things back in the day.