I'm having a hard time isolating a short ***Solved***

Thank you for your help.

I've been trying to locate a short somewhere in the stop light circuit for an hour or two most days after work. I keep blowing the 10amp stop fuse under the hood when I press the brake pedal. Most of the Tacoma is taken apart and I've disconnected almost every plug/connector in the truck to include behind the dash. All while using a light bulb in the fuse location with the brake switch hanging to simulate a pressed pedal. The light only goes off when I press the switch/ open circuit. I feel like I'm missing something. I have gone through the wiring diagrams, it's been to a shop that I trust, they cold not find the short.

Nothing new installed, all my aftermarket stuff is run to an auxbox. There is nothing on this circuit and I disconnected all my aftermarket crap for the diag just in case, it's all sitting in the garage.

What I have done-- new tail lights and factory bulbs, my housing were broken, removed the 3rd brake light, pulled all my aftermarket crap and have the interior about 50% off to include the dash and the headliner. The trailer plug is disconnected to rule it out.

What I find interesting is with the PowerProbe ECT the signal is changing direction depending on the wire it reads from the switch.

Blue wire signal points up the wire



Red Wire in the same location it points down


At fuse box, in the fuse if I leave the relay in it reports a short



Relay removed is an open circuit


I have to be missing something. With the relay removed I get no hits anywhere on the truck using the probe.
I have a couple different switches and relays that I have tried. I also have a fuse saver that trips instantly with no delay. I have also ran the probe from the tail lights and the relay with no luck.

No new codes with a fresh fuse, once the fuse pops it throws an ABS code. Older codes are present due to the aftermarket seats so there are occupant codes and SRS codes which have been there from when the seats were installed in like September.

I could be doing something wrong so if you guys have any suggestions please send them my way.

Thanks again.

 

What size bulb are you using for your "fuse"?

I've not had alot of luck using those short tracers but the reason the arrow is different on the 2 wires is it is following the direction of current flow.

The signal also goes to the PCM and ABS module, while it's unlikely the short is in one of those it wouldn't hurt to unplug them to rule them out.

I've had the best luck finding shorts by using a headlight bulb in place of the fuse and wiggling wires/unplugging stuff but sounds like you did alot of that already.

 

Thanks for the reply. I was thinking about it late last night and it hit me I had the switch plugged in so the current direction is correct.
The bulb I was using was a small 194 bulb, lots of wiggling and unplugging. I did unplug the ABS and the PCU, the bulb stayed lit.

 

I'd go to a headlight bulb like a H11 (just have to be careful of where you place it so it doesn't touch anything and melt it), they run around 5 amps which is well under the 10 amp circuit rating but high enough to not have a false positive.
Then go around with an amp clamp or even maybe a thermal camera if you have access to one to see where the current is going.

 

Thanks for that, I do have a thermal camera. I'll give it a shot.

 

Does the fuse blow only with brake light bulbs installed?

 

No, it will blow with the bulbs installed and uninstalled. I removed them both at the harness, still blows the fuse.

 

Does it only blow when the brake pedal is applied? Or as soon as you install the new fuse?

 

Yes, only when the brake pedal is applied. Once the switch is removed form the brake pedal housing, it simulates pressing the pedal.

 

@Dm93
@caribe makaira

Tried the H11 and a thermal cam.

First 2 pics light off, not stepping on the brake reading 12.8 on both sides of the fuse.


Next 2 pics light is on, stepping on the brake pedal. It reads 12.6 on the front most side of the fuse, closest to the grill. Then it reads nothing on the side of the fuse closest to the firewall.





also noticed this with the thermal cam. I believe this is the certification ECU or the main body ECU?


here is what it looks like


I'll be getting back into it tomorrow. Any ideas from you guys would be amazing.

 

I looked at the diagrams.
Power goes to the following AFTER it leaves the brake pedal switch.

1. Skid Control ECU w/Actuator
2. Combination Meter (Cluster)
3. To J7 Connector to the following
... 1. Shift Lock
... 2. Certification ECU
... 3. Towing Brake
3. EB1 connector to The rear stop lights
4. 1F/1H connector to the Center Cab light

Have you disconnected any of those to see if the short persist?
Test those locations?

 

I believe I have disconnected each of those but I will look up each one and make sure to disconnect them one by one tomorrow.

Many thanks.

 

Unplug them all. If the short goes away plug them in 1x1 until the short comes back till you find which causes it. If the short persists then you know it’s not those.

 

Here we can all be on the same page.

 

Have you removed the Stop Relay?

 

Yes I have, pics are in the original post have it removed and what it's reading.

With the relay removed its open, relay in reads a short. According to the tool.

 

Thank you very much, I find these diagrams have way more information than the nice colored ones.

 

I like them because you don’t have to look at 5 different pages like the colored ones.

 

Remove relay again, press brake pedal. Does it blow the fuse?

 

Just confirmed, with the relay pulled the fuse does not blow.

Here is a little data collection on the fuse block at the relay. Is there anything here that stands out to you.