I know but they would remain on with the ignition off and even out of the ignition because they have constant battery power remember? Look at the diagram again.

Time for a blunt maybe some others can give you some other options. I'll check back tomorrow. Good luck!

there's only you man!

triple checked the switch, removed it from the power plug, same issue, so yes, getting a constant power supply. had hoped it was that relay.

i'd also like to understand the suggestions recommended in post #15.

ACC is devices you can use without starting the car like radio and headlights, etc. On is normal driving poison. Start activates the starter then flips back to on after started. I thought it would be the relay too. The problem must be somewhere in that circuit. I would make you a quick video on how to find where the problem is but this site won't let you do that and it's hard to explain in detail with text. Very simple though.

Sorry, missed this part.

i could provide you an email address to send a video clip to.

tested all of the standard fuses (type A) under the hood and under dash for continuity (multimeter). all beeped. did not try the larger box fuses (type B or C ) or relays yet.

That's good to see you have decided to test the circuit! Do the same for the ones inside by the parking brake also. Then you can apply that same basic process you used on the fuse to the rest of the circuit! You're basically doing the same thing with the rest of the circuit looking for bad wires, open ground, harness plug terminals, etc. Break it down into sections from one intersection to another and test for continuity and/or voltage when the condition is necessary. Key on/off. Good place to start is in the middle of the circuit like the relay box most easily accessed and possibly a problem area. Don't f_ck the female terminals up careful not to spread them. The second diagram posted on the beginning shows the harness terminals to test from the switch. Make sure your harness matches the one in the diagram with the layout and wire color..

Is this a factory trailer plug harness? If so do you have a V8 or V6? IIRC the V8's have a sub-harness for the trailer wiring, so you can look under the vehicle find the sub-harness connectors (should be be behind the bumper up by the spare tire on the driver's side if I remember correctly), I don't remember if the V6's had a sub-harness or not.

IF it's an aftermarket trailer harness, that could be a possible issue; I have seen lazy wiring, poor taps, and corrosion cause weird issues as a result; most aftermarket trailer hitch shops will pop one of the tail lights off and tap the wiring for the trailer plugs.

I would also pop both of your tail lights out and inspect the wiring, bulbs, and the sockets. Improper bulbs, corroded sockets, and/or wiring could cause your issue (you didn't say whether or not the brake lights stay on with the headlights on or off, or did I miss that?)

On '03~'05 4Runners, they use a dual filament bulb for the tail light and brake lamp, they also feed power from the body harness through the sockets and wires in the tail light. In '06~'09 models they updated the tail lights to have LED panels for the tail light and brake light functions, but the utilize the same connectors, socket layout, and passive wiring that the older ones did.

You have an '07 V6 right? Have you ever had the tail lights replaced? We had a 2nd Gen Prius and a 2nd Gen Tacoma that had similar issues a month or two back; both had aftermarket tail lamp assemblies (the Prius had knock-off factory style tail lamps and the Tacoma had some ricer style ones) and both had some sort of internal issue with the LED circuit that backfed into the lighting circuit and caused issues.

thx for the suggestions! i have an '07 v6. factory tow set up. i checked the two tail light bulbs (both original). was looking for a middle bulb, didn't realize LED? gonna check the bulb harness in each light assembly for issues. looked under the rear, didn't visually see any issue with tow harnesses.

So what I would do is unplug one tail light and see if the issue stops, if it doesn't plug the tail lamp back in and unplug the other one. This should rule out any weirdness in the tail lamp assemblies and let us know we're likely still looking for an issue in the main portion of the circuit up front.

and what about the third stop light?

If you feel comfortable pulling down the headliner in the back a little bit the connector for the back door harness (BD1) should be accessible on the driver's side of the roof panel by the D-Pillar.

Otherwise we'll have to just assume that the 3rd brake light isn't faulty for the moment if you're not comfortable with that.

Note- If you do unplug the rear door harness, you'll need to relearn the rear window position (Roll it up and down 3 times in a row) so that auto up/down functions work.

just checked the tail lights. connections look clean, unplugged one, then the other, normal, plus third light stayed lit. climbed under, didn't see anything abnormal with the factory tow light connections.