'04 Headlights turn on when it rains!

Hello All,

My 1st gen Tacoma has been having headlight issues lately. The relay was sticking and the headlights would not turn off even with the switch off and the keys out of the ignition.

I replaced the relay and the headlights were functioning properly for a while but now every time it rains, my heaedlights will just turn on by themselves! After a good rain last night I came out of my house this morning to find my headlights on.

I'm thinking water is leaking in somewhere and shorting the headlight circuit, anyone have experience with this? PLEASE HELP!!

Thanks!

 

Oh that's a good one. I think you're right: Somehow water is getting in and shorting power to engage the relay

Here's a thread with some wiring diagrams that may help: https://www.tacomaworld.com/threads/2001-tacoma-bright-lights-dont-work.634344/#post-21809738

 

Thanks! I am going to investigate further this afternoon and hopefully recreate the wet conditions with a hose. I sometimes get water leaking into the cab after a rain as well, but it is not nearly as frequent as my headlight problem.

 

Maybe go with a small spray bottle.

 

If you have HIDs the relay might have water inside it and might be shorting out. Therefore the lights will turn on automatically.

 

I had a leak at the windshield, and water would follow the wiring down to the integration circuit relays, which are on the back side of the inside fuse panel.

 

Just gotta find a way to dry out that relay and waterproof it once dried out. Otherwise this will happen every time its wet. I dried out my relay and then duct taped it. That was my method of keeping water out of it. To each their own though.

 

I would suspect Body ECU. In your Tacoma year/model this is an electronic board that at the end shorts pin 13 to the ground.



Open that box and see if you have any signs of corrosion or other water damage. This is electronic board meaning low voltage and very low current elements, so moisture can play tricks on its functionality. Any other circuits run on to much higher current for water shoring them out.

Luckily in my truck year (95) Body ECU (it was called Integration Relay then) does not control any vital things in the truck (only seat belt chime, door open chime and lights, or "lights on" warning buzzer). The worse thing it cam turn on is dome light .

Almost forgot, that unit is also responsible for electric locks (all years with electric locks), so it that thing goes nuts it may actually unlock the car on its own .

 

Thanks Guys! Awesome leads to follow, I'll update if I get it resolved!

 

This is located behind the fuse block inside the dash left of the steering wheel?

 

Yes, it is located behind the panel where you see these fuses. Just the fuse box, Junction box and Body ECU is the whole one unit. I have not seen junction box in later models, but in my 95 the integration relay part is bolted to and sticks out of the front of the junction box. I don't have any good picture but you can see it on this one (arrow pointing at that white thing):

 

SO! There was definitely water on and around the Body ECU, and I pulled the dash apart to trace the leak. It looks like it is coming from somewhere around where the windshield and the body meet in the bottom drivers side corner. Looks like a little bit of water has been dripping down the inside wall, although when I poured some water on the windshield and body I could not get a visual on water actually entering the cab.



There is a small amount of corrosion on the relay in the Body ECU.

Anyone have any thoughts on where my water entry point is?

Thanks All!

 

I believe that's an intentional safety feature. Many jurisdictions require your lights to be on when it's raining.

 

If you're lucky enough the Hazards go off too.

 

smother some fluid film ff that should chase water and waterproof them maybe idk

 

Mine was collecting water on the back/top of the white fuse block. It will hold moisture around multiple connections

 

Electronic circuit don't react well to water or moisture. That's why Apple uses "water damage" excuse to void a warranty when customer comes for repair with phone and laptop.

 

In the socialist republic of CA, you need to have your lights on when it rains... If not... You guessed it, ticket

 

More of a job for dielectric grease.

 

i thought ff answers all 1st gen ills
what am i doing