Electrical Problem: Brake lights on with Tail lights (1 Viewer)

[kenton]

Help, oh 80 gods,

My brake lights (both sides and high-mounted LED) turn on when my tail lights are turned on. When I press the brake, they get slightly brighter. When my tail light switch is off, the brake lights act normally.
Diagnosis:
I've pulled each of the tail and brake light fuses. With the tail fuse pulled, the brake lights work normally. With the brake fuse pulled, the brake lights still go on with the tail lights.
When I turn the vehicle off with the tail light switch on, both go off. If I then turn the tail light switch off and then on, the tail and brake lights go on.
In other words, the brake lights are acting like tail lights as well as brake lights. As if I have a short circuit between the two circuits, somewhere downstream of the fuses and switches (both brake and tail light).
I have physically wiggled the harness at every point I could reach: the high mount brake light, right behind each side light (after removing said light), inside behind each light (after pulling out the interior to reach it), underneath along the bottom back, and up by the ECU. Nothing had any effect on the brake light, no flickering or anything.
I have a trailer light I spliced in a year ago, I checke-wiggled and even removed some of those connections, no effect. There used to be a trailer box underneath by the trailer hitch that was removed over a year ago, I check-wiggled those old wires, no effect.
I noticed the wiring bundle going from the rear drivers-side to the rear pass-side, going into the pass-side rear quarter panel, didn't have its grommet seated into the metal hole, so the wires were laying on the metal. I vigorously moved those wired, and put the grommet back in the hole. No effect.
I'm going crazy trying to figure this out. Every time I turn on my running/tail lights, my brake lights are always lit. It really sucks now that winter is approaching and most of my driving is at night, so have essentially no brake lights.
I really dread taking it to a mechanic, but I'm stumped on a good diagnostic.
Thanks,
Kenton

 

[landtank]

I'd suspect something in the trailer harness. I'd do a complete removal of the controller and not just wiggle/disconnect a few wires that you have already done. That's really the only logical place that power from the tail lights could likely get routed to the brake lights.

 

[CDN_Cruiser]

I agree, if this is the only change you have made to the system, and it just started happening, you likely have a problem with the trailer wiring. It should only be a few wires connecting to your main harness.

Disconnect all the wires and make sure the original (factory) wiring is intact.

See if that fixes the problem and then you can go from there. It may not sound great, but with other wiring in the circuit, it's hard to do any diagnostics using a wiring diagram.

Cheers, Hugh

Edit: Did this just start? How long? Any other changes you've made?

 

[kenton]

Thanks guys. To clarify (as I re-read my message): the brake and tail/parking lights come on/off in unison. When I press the brake, the dash lights come on, the clock dims, etc.

This just started recently (a week ago) roughly. It might be intermittent, since I usually always have my running lights on, this problem isn't noticable to me unless I somehow notice that my brake light is always on. I only just started realizing/attacking the problem this weekend.

The trailer harness (a Uhaul special) I spliced in this spring, and the lights problem just cropped up. I disconnected the brake wire splice, with no effect-- I very much doubt any other part of the trailer harness could be an issue, since I had it all in front of me inside the rear pass fender, it is fairly simple, and the remaining connections (after removing the brake) I can't see how they could short the brake and tail. But, if I don't think of something else, I will go back over this wiring again.

So I guess no one else has seen such a problem? Darn, I was hoping it was one of those "yeah, often 97 FZJ's will rub the wiring harness above the engine at the firewall, and short X and Y..."

<sigh>
Kenton

 

[CDN_Cruiser]

Warning - I actually really don't have a clue about this stuff, aside from messing around a bit with some of the wiring and having a FSM (=little knowledge = highly dangerous)...the only reason I have some thoughts are based on my recent wiring experience with a light and looking at the trailer wiring some monkey put in the truck.

First, you REALLY want this to be the trailer wiring. If it's not (1) you will likely spend a ton of $ having someone diagnose the problem or (2) you will need to get a wiring diagram and a multi-meter and slowly tear your truck apart as you trace all the connections for both the brake light and running light circuits.

When I looked at the trailer wiring in my truck it was VERY poorly installed. On my system (a small box with truck side and trailer side) there were something like 4 wires to splice into the system. Again, I would remove the ENTIRE system and then see if you still have a problem. On the wiring diagram, they (Toyota) show a trailer splice point just upstream of the tail lights/brake. This would suggest to me that this could be the source of the problem.

If you don't want to do that, you should probably start by testing the rear taillight relay (DS kickpanel according to my diagram), brake switch, check the combo lights for shorts, etc

Good luck

Cheers, Hugh

 

[landtank]

No offense Kenyton. but if your skill level is at the "wiggle and check" level you might want to re-evaluate your ability to install the kit in the first place. Put the truck back in it's original state and then check it's operation, you need to base line the trucks wiring first.

 

[kenton]

problem resolved-- unusual bulb condition

Rick, believe me when I tell you that 'wiggle and check' is an effective, initial part of a larger suite of electrical diagnostics. (Or don't believe me-- this is described in the Toyota electrical wiring book.) How my embarking on the start of my diagnostics journey led you to conclude that it was the extent of my skill level, is a leap of logic I'd be interested to hear you explain. Also, regardless of skill level, you shouldn't discourage people from trying things out and learning how to install things. (while staying consistent with personal safety, of course.)

Finally, I disagree with your 'return it to base line' statement. For many (most?) people, returning their vehicle to original electrical state is impractical and would require hours or days of work. And even then, who knows if in the process of removing splices etc, a new problem isn't created?

Anyway, for those who have read this thread, I wanted to follow up with the resolution. I've diagnosed many electrical problems over the years, and this was a new one on me. Basically, the DS tail/brake bulb had dropped its brakelight filament so as to shortcircuit the brake and tail circuit. The bulb appeared to operate normally (on for tail or brake, brighter for both), so I missed that on my initial 'walk-around' visual check, and even further visual bulb checks. It wasn't till I traced down the problem to that section and started examining each item carefully, that I saw it.

Regards,
Kenton

No offense Kenyton. but if your skill level is at the "wiggle and check" level you might want to re-evaluate your ability to install the kit in the first place. Put the truck back in it's original state and then check it's operation, you need to base line the trucks wiring first.

 

[landtank]

What page number in the EWD is the wiggle and check described in a short circuit? Also to base line the vehicle by removing the trailer harness control is 2 plugs, less than a minute.

 

[semlin]

Hmm, just troubleshot my faulty brake lights last night. It is not so hard to do if you happen to have just removed all the seats, carpets and centre console .

AFAIR there is no place for the stop lights and tail lights to cross over in the Toyota stop light system so I'd say 99% likelihood it is the trailer harness box. disconnect it and see.