Weird Electrical Gremlins?

Hey y'all - I recently picked up a 2004 double cab and have spent the last few months baselining all neglected maintenance and undoing essentially everything the previous owner had done (starry headliner, removed various cables/switches/etc). It's got 260k miles or so, and is in pretty good shape all things considered.

Every since I bought the truck, I've noticed that when I lock it using the OEM key fob, multiple lights will flash (along with the corresponding audible beep): side marker lights, rear blinkers, rear license plate lights, and interior dash lights. It's also a higher "beep" noise than normal, almost like an aftermarket security system. My headunit will flash black when I press the brake pedal, my blinkers will go slow then speed up sometimes (all by themselves), and just today I got a check engine light for P0705, a transmission PRNDL code.

After some Googling, other Toyota owners have noted some of these electrical systems share the same circuit/fuse - maybe they're connected somehow? The alternator is charging at 14.5V, car battery is a few years old. I'm thinking whatever the previous owner did to make multiple lights flash (aside from just the normal front/rear blinkers) is messing with this circuit. Any ideas/experience?

 

Update: I've narrowed the problem down to my rear driver taillight. I added a backup camera a few months ago and soldered to the taillight hardness ground and reverse bulb. It was acting finicky recently so I unsoldered the backup camera wires and essentially restore it back to stock. This is when things got weird:

- when I have my left blinker on (whether I'm turning left or have my hazards on) and I press the brake pedal, the blinker begins to blink rapidly like a bulb is out. I can only replicate this behavior when the left blinker is on AND when I'm pressing my foot down on the brake.
- when the blinker is on and the brake is applied, the BRAKE light will begin to flash rapidly (like the blinker without a bulb). If i take my foot off the brake pedal, the blinker flashes like normal, at a normal speed. All the while, the blinker and reverse bulb glow oh so slightly - like they're lit, but barely.

I moved the passenger housing over to the driver to see if it was a taillight assembly issue, which is not the case. The passenger side taillight did just fine on the driver side, and the driver side taillight was acting up on the passenger side.

Any ideas? I am not an expert when it comes to wiring, and I don't know what the previous owner did. This is, however, a new issue, that I might be to blame. The original taillight wires were never severed when I soldered to them - their insulation was stripped back on one side ONLY for me to solder to, that's all. I've since wrapped up the wires with electrical tape (and removed the backup camera wiring entirely).

 

Here are some other pictures to help illustrate this insanity. The first picture shows the insulation I shaved back to expose copper. This is how the wires currently look, except they're now wrapped up in electrical tape. The second picture is what I see when I push in the brake, with no blinkers engaged. The driver side blinker faintly glows when the brake is pressed, like it's receiving power? What is going on!?

Again, no original wires to the body/taillight harness were severed. Maybe a bad ground? Shorted wire somewhere else in the harness?

 

Here's the second picture showing the driver blinker glowing faintly when the brake pedal is pushed down:

 

Do you have regular bulbs or LED? If not LED are you sure it's the correct bulb type. For all of the bulbs.

 

All bulbs, I just changed them all out for new ones this morning (thinking it would make a difference - it did not).

1156 turn signal, 1157 brake light bulb, 921 backup bulb

 

Those symptoms really sound like the drivers rear tail light has a bad ground connection. I would chase that ground connection from the bulb holders to the sheet metal, looking for any corrosion, marginal connections, or broken wires.

 

Is the driver taillight physically grounded somewhere nearby? Or just grounded elsewhere through the main harness.

I removed the taillight again this morning, and removed the first 2 feet or so if it’s wiring harness from the truck so I could inspect - everything looks in order. There are two ground wires in this harness, with no visible damage/scuffs/etc. I followed the rest of the harness back into the body and it looked fine as well.

Are there common rub points I should be looking for? Is there a way to me to located a break in an individual wire (like a ground in my case) - similar to how they energize and locate individual wires underground?

 

https://charm.li/Toyota/2004/Tacoma...osis/Diagrams/Electrical Diagrams/Brake Lamp/

The diagram shows the grounds for the brake lights at the right and left footwell area behind the panel. I find this hard to believe that they would run a ground for the tail light all the way to the front of the truck.

 

Yeah I could be mistaken, but I did not find any dedicated grounds in the taillight area.

I just purchased a cable tracker to send a tone through the driver taillight ground to see if there’s a break inside the wire, with no visible damage.

Is there a ground anywhere beneath the bed/rear section of this truck I’m missing? So strange the issue is only on the driver side. I’m convinced the issue is in the 3ft of harness dedicated to the driver taillight. I’ll have more time this afternoon to find the break in the wire (if there is one).

 

Check your trailer connector wiring as well

 

I do believe all the lights share the same ground and are spliced together at the tail lamp but dont quote me. Check the bulb socks inside and behind for corrosion or broken wires shorting together.

 

I took a picture of the current trailer wiring while I was poking around. Does this look factory? It’s a 4-prong connector. Looks original, but couldn’t be sure.

Ignore the stray non-factory wires you see in that pic, they’re the ground and 12V wires for the backup camera that currently aren’t connect to anything.

 

I swapped the passenger taillight (the side with no issues) for the driver side, and the problem stayed on the passenger side. So it’s not a tail light assembly issue - definitely wiring.

 

All the bulbs share a ground, and the left side routes to the right side and grounds to the rear of the frame.

 

Do you have a picture of where this ground is at the rear of the truck?

 

You sure you have the correct bulbs in the correct spot? You dont have a brake/tail bulb in the turn signal socket?

Edit: i see you swapped assemblies and nothing changed.

 

Lucky for you i have a double cab 1st gen let me take a look

 

Please do - I’m not with my truck right now otherwise I’d be crawling all around it with you!

 

Here’s an off topic question: when you lock your Tacoma with your key fob, what lights flash indicating everything’s locked? At the front of the truck, my side marker lights will flash, at the rear, my brake lights and license plate lights will flash. My gauge cluster also flashed in sync with everything. Not sure if this is normal. It certainly isn’t in my previous experience with Toyota’s. I thought it was always blinkers front and rear that would flash only