2007 Base Tacoma Tail Lights not working-blown fuse

I recently found that my tail lights are not working. The headlights, turn signals, brake lights, and hazard lights work fine. I have checked the rear wire bundles for possible pinches and or abrasions, and have not found any problems. I disconnected the rear tail light assemblies at the connectors, and removed the license plate light bulbs, installed a new fuse, and turned on the lights. This burned out the new fuse. I also checked the wire bundles in front leading to the front lights, and did not see anything unusual. I am thinking the problem could be in the switch, but would like to be able to positively identify this as the problem prior to ordering and installing a new switch. Can someone help me in how the check the switch, or give any other troubleshooting assistance?

Thanks, Tom K

 

I can tell you 100% it's not the switch, all the switch does is signal the Body ECU to turn on the Tail Relay which powers the Tail Fuse.
You must have a short somewhere in the wiring, a bulb socket, or a connector.
Do you have a towing adapter harness installed? Those have been known to short out.

 

The truck is a base model, and there is no towing adapter installed.

Thanks, Tom K

 

This might help, IF we have to go that far.

 

One of my earliest tests was to check for ground. I removed the tail light assemblies and disconnected the plug. When I checked between the ground wire (which I believe is the white w/ black stripe) and the tail light wire (green), I get connectivity. I thought I had found the problem, but when I check the other wires against the ground, I also get connectivity. When I did this, parking light bulbs had not been removed. When I check (with the tail light assemblies unplugged) between the contacts on the tail light socket with the bulb removed, I do not get connectivity. If I remove all six bulbs (parking, tail, and license) will that help in finding the short?

Thanks, Tom K

 

Shorts can be a challenge to find but since yours appears to be a dead short it can make things easier.
You could disconnect all your tail and marker lights and if it still blows the fuse you can install a test light in place of the fuse and start wiggling wires until you get the light to flicker to find the short.

 

No, removing the bulbs won’t help.
Removing the fuse and checking for continuity to ground would though.
Obviously, you need to be on the correct side of the fuse block. (The one that does NOT have power)
Don’t jam the probs into the fuse terminal too hard. Or else you’ll risk opening the terminal up too much and cause a loose fuse later.

 

https://www.youtube.com/watch?v=nzRHDOszdUc

 

I did some checking (flexing wires in various places) using the resistance scale on my vom. I was checking between the unpowered side of the fuse, and ground. I couldn't find anything. Out of desperation I decided to pull out the recently installed aftermarket stereo. There was a plug from the factory unit that was not being used, but had some cut wires hanging from it. I removed the unused plug, and rechecked using the ohm meter. On the Rx1 scale, the reading had been 0 ohms, but after removing the unused plug behind the stereo, the reading was now about 3 ohms. I put in a new fuse, and the lights are now functioning normally. I'm not sure how this was causing the short that was blowing the tail light fuse, but it must have been.

Thanks everyone for your help,

Tom K

 

Pretty sure the taillight fuse/relay powers the backlighting for the radio also.
That’s probably what caused it.

 

I know it does on a '95 Dodge Dakota! Maybe that's common. Years ago I installed a new radio in that truck for my son and ended up having to disconnect the lead from the new radio labelled 'lights'. Otherwise the fuse would blow for the taillights - but the radio still had lights if I recall correctly, just not corresponding to the instrument panel dimmer control setting.

Good find @TomK. Good schematics @Dm93. I assume these would be the same for a 2007?

 

Yea I saw you had an aftermarket radio but I didn't think about it, the Tail fuse does indeed feed all the interior backlighting.

Yes the Tail fuse feeds the illumination circuit as well, that's what I hate about Toyota diagrams they have them broken down by circuit even though different circuits have wires in common they don't show up like that. You have to deduce it by looking at wire colors and pin numbers across multiple diagrams.

05-07 wiring diagrams should be pretty much the same, things didn't start changing electrically until around 08-09. I can get most OE diagrams for 2nd gens but there are gaps in Mitchell where they don't have OE diagrams and show only their redrawn diagrams which aren't always accurate.

 

I have to be honest, the only reason I knew the tail fuse was linked to the radio was because aftermarket radios, if hooked up wrong, are know to blow the rheostat in Toyotas.
I believe it’s the orange wire you don’t want to hook up. I can’t remember.

 

Yea the dimmer circuit works differently on Toyota than most other vehicles in that the dimmer knob controls the ground side instead of the power side.

 

I see the Illumination file has several pages. That's why with my son's truck I actually made my own summary diagram maybe with Visio for the lighting wiring so it could be all on one page.

Oh wow hate when that happens!

Interesting - maybe the case with the '95 Dodge Dakota I worked on. Good to know for future reference. I can see getting an aftermarket stereo at some point.

 

It's interesting, it shows 2 illumination circuits for the radio on a 95 Dakota. One is direct power from the headlight switch and the other goes through the dimmer switch, diagram is redrawn so take with a grain of salt.

 

Wow, you could still pull up info on a '95 Dodge! Same engine as my son's had. If I only had that schematic 17 or so years ago! I'm at work now but I'm 99% sure in my schematic I have a note not to connect the BLK/YL. Like you said, the radio lights are shown to have 2 sources, also the OR wire. Maybe because of that is why the BLK/YL should not have been connected. It appears the Dakota's radio lights had a conventional +12v feed from the dimmer unlike the Tacoma's ground connection that was varied in the dimmer control. As noted, something to keep in mind if/when replacing the factory Tacoma stereo.

I'd imagine every modern vehicle's wiring diagrams will now show some reference to a 12v to 5v regulator for USB outlets.

 

Yea Mitchell has info going back to the 80s although most of their wiring diagrams are redrawn which kinda sucks, I prefer OE diagrams except on euro stuff.

USB sockets are typically connected directly to the radio.