Turn signal comes on solid when pressing brake on my 2007 Tacoma

I have read a thread about this problem and have verified that all bulbs are working, I disconnected the trailer harness and I checked all wiring at the left rear turn light. Everything seems to be in order. I don't know how to check the flasher. Any advice on this or other possible causes? Also, is this something that could cause a serious problem or just a nuisance?

 

I'm working from memory here and this has been a long time ago. But I think it is possible to get the wrong bulb installed and cause this. Verify that you have the correct bulbs for both the brakes and turn signals.

 

I had a similar problem and there was a short on the harness feeding from the driver side to the passenger side. The right blinker would come on solid when i'd hit the brakes. I had an aftermarket 4pin towing harness that i added and i botched the install lol and it started rubbing on the bumper until finally it rubbed through. You might go back through all your wiring again even though you said you've checked it.

Also, welcome aboard!

 

Voltage from the brake light circuit is spilling over into the turn signal circuit. Check for incorrect bulbs installed, check for a melted bulb socket. check for a short between the 2 circuits (like two wires rubbing together)

 

Thanks guys for your responses. The bulbs are original to the truck. I checked both front turn signal bulbs and all elements look good. I also checked all the wiring I can see for shorts and did not see anything. When checking the bulbs today I discovered another thing. The front park lights don't come on when the park light is on at the light switch. The back ones work properly. I checked the fuse for the turn signals and it is good. I agree that there appears to be some sort of spilling over from the brake circuit to the turn signal/park light wiring. But, I am at a loss to find it. I had a skilled mechanic install a towing/braking wiring kit over a year ago but haven't had any problems until a couple of weeks ago. I will probably take it back to him to diagnose if all else fails for me.

 

Probably a rusted ground connection, pinched or broken wire, or oxidation.
Get a test light and start exploring.

 

This, most likely a poor ground.

 

You could still check the bulbs, see if one is glowing dimly compared to the others.. if a filament gets weak and bends over and touches the other filament that's a short right there

Edit: but now that I think about it, the turn signal bulbs aren't close to the brake light bulbs in the housing.

 

Does the turn signal come on anytime you step on the brake or only when the turn signals are on and is it one or both sides?

 

I will recheck the grounds. The only one I found looked good. The left turn signal indicator on the dash comes only when I press the brake and goes off when I release it. I do have an after market towing wiring kit installed but that was done over a year ago with no problems until this month.

With the brake off, both front park lights do not work in park light mode but do work in turn signal mode. Back park lights and turn signals work.

With the brake on, both the front and left turn signal lights come on solid without the turn signal switch being on. When the turn signal switch is turned on to the left, the lights stay on solid without blinking.

I am hoping a real wiring guru out there will see this and come back with an "Aha, I know exactly what the problem is"

 

Out of curiosity, what happens if you pull to stop lamp fuse.
Then try the turn signals?

More than likely, you’re going to need to start unplugging connector for the turn signal circuit.
Process of elimination method is how I’d approach it.

For now, I’m going to suspect the towing kit.
Depending on the kit, some have there own control box, and they can do weird things if they start to fail.

 

Have you had any issues with water intrusion in the cab that you know of? The only thing that they have in common that I can see in the diagrams is they all go through the drivers side junction box (fuse box)/Body ECU, I think I'd go there and unplug connectors and look for corrosion and/or burnt terminals.

 

If this install was done with automotive connectors, that could be your problem. They'll cut completely through a wire, cause shorts.

As already mentioned, a bad ground is possible. But Im pretty sure the Tacoma's use ground wires instead of a grounded housing.

Just because you replaced the fuses doesn't mean one immediately popped. Test the one mentioned above, don't just look at it, test it.

 

I am not sure what a "stop lamp fuse" is but will assume it is the fuse for the brake lights. I'll try pulling it to see if that works.

I don't know of any water intrusion I have had in the cab or engine compartment.

I'll look to see what connectors I can find that I have not already tried and disconnect them to see what happens.

Thanks to all for your suggestions. Wiring is my weakest area of automotive repairs so I appreciate all the help you have offered.

I will let you all know if I get the problem resolved.

 

To start, you should get a decent multimeter, if you don't already have one. You don't need to get a high dollar fluke. There's plenty of decent quality brands, es, amprobe, and such. If you get one with a built in amp clamp, even better. Just make sure the amp clamp can read dc amps, many don't so it should specify that it does. Features like peak hold, back lighting, display big enough to see are all good to have but not extremely necessary. From there you can add different leads, aligator clips, wire piercers, back probes and such. For leads, I've found the fluke ones to be fragile. I switched to extech tl726, they're longer, thicker, last much longer. I have the fluke 87v multimeter and i1010 amp clamp. Both are very expensive and have never failed me except when the battery died. I shopped for models that take easy to get 9v batteries, instead of some odd fluke specific thing. Then it's just a matter of playing with it and learning how to use it. What's nice is if you shock yourself with your car, it doesn't hurt all that much, even with wet hands, except for a spark plug shock.

 

Something similar to this used to happen with my old T-100 when everything got really wet, like a lot of slush on the road. I finally got under it and disconnected each connector on the wiring harness (under the bed) sprayed them out with WD-40 and reassembled them. Never had a problem again.
Not saying this will fix it but it's something cheap and easy to try.

 

Great idea. Something I like to share, wd-40 I heard somewhere is a military numbering something, means water displacement attempt 40. So I guess if the previous attempt were successful, we'd be calling it wd-39.

 

That is my understanding as well.

 

It is, I call it Stop Lamp because that is what Toyota calls it.
And that is what it is labeled in the fuse box.
Normally, I do call it the brake light fuse. But when helping people I don’t know, I try to use the correct terms. It helps to keep from confusing people.

 

Cool info:

https://wd40company.com/our-company...nds for Water,Missile from rust and corrosion.