Help, I have an Electrical Nightmare

I have a manual 6-speed 2007 Tacoma, base model -

So a few weeks back I noticed that both my back taillights were out, but the brake, reverse and turn signal lights were still working. Replaced the bulbs, nothing. Replaced the 10a fuse under the dash, nothing. Tested for 12v at the rear harness where the car's wiring plugs into the tail light. NOTHING. Upon further inspection, I found the daytime running lights and the rear plate lights also were out.

So I start thinking, it must be the aftermarket rat's nest of a "tow package" UHaul or someone installed for the previous owner. The thing was electrical taped and zip tied to hell! After undoing all that mess, I found a nasty number of vampire taps and bad splices. I figured it was best to remove all of it completely, and sure enough, there were three wires that had split.

I hooked them back up (they were three different colors, so I figured I could safely assume what goes where) with some butt splices and heat shrink tubing and eagerly turned on my car. and that's when everything got weird...

When the car is in reverse, my driver's side brake light works! but not the passenger side. The left turn signal blinks really fast, like double time, but it is the brake light that is doing the flashing while the signal bulb weakly illuminates.

If the car is not in reverse, the tail lights don't work at all, but brakes/signals/ and R lights still do. When I put on the left turn signal, however, causes a weird beeping to come from the under the dash, similar to the key in ignition alarm that beeps when you have your door open.

Does anyone have any idea what I should try next? I think I need to peel back all the wire loom and see if there are other places that those clowns cut into the factory wiring

 

Bump. Should I post elsewhere?

 

Electrical gremlins are hell. Can't think of anything besides what you already know, that someone wreaked havoc on your wires. Check grounds, check for taps that severed wires, check for taps and severed wires underneath the dash, who knows what other wiring contraptions they've done

 

I don’t know enough to help, but posting in the 2nd gen forum is probably a good start. It’ll get more attention that way

 

It’s a complicated one and I’m guessing that’s why you haven’t received many responses. Without being there and seeing what you’re up against it’s going to be tough to offer any specific advice. Look for broken and shorted wiring is where I would start.

 

It's hard to internet diagnose something like this. Likely a major splice or open circuit causing the issue for power to only come through when reverse is engaged.

It can be impossibly hard to diagnose, are fuses getting power? Don't just check the fuse blades, check to see if the blades are getting power on both terminals.

Are you getting ground to bulbs at all times?

You may just either pay someone to fix it, or farmer wire a new set of wires from, the junction box back.

 

Yeah sounds like crossed wire too and as a result you’re not getting a ground. A lot of the symptoms you described sound ground related- kind of like a trailer when you don’t have a good ground- shit gets weird!

 

I did not chime in earlier because it sounds like several different problems all together. I do know that the rapid blinking of the turn signals is most times caused by a bad bulb or socket in the system.
It all can be fixed it will take some time. work on each problem separately.
A repair shop will just run up labor hours on a job like this and you will probably have more issues right away or shortly after it leaves the shop.
Wish I lived closer I would love to fix it for you.

 

Check at the back of the truck, either behind the tail lights, or under the truck for additional messed up wiring.

 

Yeah, like @TomTwo said, that fast blink is the system telling you there is a bulb not working, so that at least is a decent sign, even if you have wiring crossed.

When they do trailer wiring, they usually put a small device in that combines your separate blinker and brake lights to the single trailer light. If they tried to do something without that device, that could combine some wires that shouldn't be combined.

Are you trying to maintain the trailer wiring, or just get it back to working properly? For $20 you can get 2-day access to the wiring diagrams at https://techinfo.toyota.com, which is something I have done for previous trucks. Once I get access I save everything I can to a PDF. I don't have the diagrams for a 2007 though.

Probably best to get it back to stock working order, then figure out the proper and clean way to add trailer lighting if you need it.

 

^^^^^^THIS^^^^^^
Get the stock system back to original working order and then add a (plug and play type trailer harness)

 

I would get a Toyota electrical diagram for your year truck and for those specific circuits, there its clearly listed the wire colors and what connector/ junction they go to, location of grounds, ect. thats where i would start and check everything one issue at a time. i worked for Toyota for many years and have seen things like that pretty much on weekly basis, its not the end of the world, but you need schematics and patience.

 

Thanks for the responses, everyone! This blew up while I was away. A few updates since I last posted. I crawled under there again and double checked/redid my wiring with some nicer, waterproof butt splices and some heat shrink just to be safe. Turns out one of the repairs I had made had come loose. After fixing that the signal issues went away. But, my car now does not have tail lights no matter what gear I am in. So, kinda back to where I started, lol.

I think this is the best path forward for me. If I knew what wire to check all the way back to the battery I could isolate the problem. I will gladly pay for 48-hour access. I took the manky trailer hitch off day 1 (which did include a little box) so I should be back to stock.

I looked behind both tails and saw no bad wires or shorts. I checked for voltage at the tail light plug and got none there. I was getting a read at the fuse block on the 10a slot that powers the tail lights. I also followed the wire loom from the passengers' side tail, back and down along the length of the driver's side of the car the best I could, did not see any obvious damage.

A few people are saying a grounding issue. Is it possible a bad ground in the engine compartment could do this? Is there a relay under the hood that could go bad to anyone's knowledge

 

To check that, see if there’s any voltage between your engine block and the chassis ground (bare metal on firewall side, etc,).

 

Ok. I had a similar set of symptoms. Taillights, license plate lights, backlight behind a/c knobs. I finally figured it out after wasting $500 on a rebuilt BCM...and about 50 hours of digging and tracing wires, researching etc...the culprit...my son had installed an after market stereo and left an exposed wire for some backlighting display, that had no mate for the wire. The exposed wire was either touching another or being grounded. Either way I put a wire nut on the orphaned wire, replaced my 15th 10A fuse and now everything magically works fine. Hope this helps.

 

I would just undo what you did and go one wire at a time.

If you have someone else to help you that would be even better; have them step on the brake, use turn signals, etc.. one at a time while you use a test light to see what wire is doing what.

 

Good luck.