Uploaded June 2026 | Updated September 2026, 3 weeks ago
In this Subaru Forester no brake lights diagnosis, a simple blown fuse test turns into a smoking electrical failure right in the middle of troubleshooting. We start with the brake light circuit wiring diagram, use a test light to check power at the fuse, confirm a blown brake light fuse, and then follow the circuit toward the rear of the vehicle to find out why the fuse keeps blowing.
The problem ends up being a shorted trailer wiring harness module tied into the rear lighting circuit. When the brake lights are powered back up, the module smokes and melts, revealing the source of the short. This is a great case study on brake light diagnosis, blown fuse testing, trailer wiring problems, short-to-ground troubleshooting, test light usage, and why fuses do not just blow for no reason.
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*In-depth classroom lectures based on the material in my book
*Case studies with real vehicles brought into class
*Troubleshooting using proven diagnostic methods
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*Fundamental training in automotive electrical, electronics, and drivability diagnostics
📘 Want to Learn More About Diagnostics?
Check out my field manual, Engine Performance Diagnostics, available as both an eBook and paperback at:
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⚠️ Disclaimer:
ScannerDanner LLC is not responsible for misuse, unauthorized changes, or incorrect application of any information provided. Always follow proper safety protocols when using tools, equipment, or procedures discussed in this video. Use this content at your own risk.
0:00 Intro
0:23 Reading the brake light wiring diagram
0:58 Testing the fuse with a test light
1:15 Finding a blown fuse
1:50 Fuses don’t blow for no reason
2:15 Replacing the fuse and testing brake lights
3:16 Inspecting the bike rack wiring
5:05 Tracing the brake light circuit
6:23 Narrowing down the shorted circuit
7:30 Testing the trailer harness wiring
8:12 Finding another blown fuse
9:31 We found the culprit
10:27 Brake lights work after unplugging module
10:36 Why the fuses blew
11:51 How the trailer module controls the lights
12:15 Final diagnosis: shorted trailer harness module
12:25 Bonus footage
In this Subaru Forester no brake lights diagnosis, a simple blown fuse test turns into a smoking electrical failure right in the middle of troubleshooting. We start with the brake light circuit wiring diagram, use a test light to check power at the fuse, confirm a blown brake light fuse, and then follow the circuit toward the rear of the vehicle to find out why the fuse keeps blowing.
The problem ends up being a shorted trailer wiring harness module tied into the rear lighting circuit. When the brake lights are powered back up, the module smokes and melts, revealing the source of the short. This is a great case study on brake light diagnosis, blown fuse testing, trailer wiring problems, short-to-ground troubleshooting, test light usage, and why fuses do not just blow for no reason.
🔧 Looking for Deeper Training?
Whether you're a DIYer, an aspiring tech, or a working technician, ScannerDanner Premium gives you in-depth diagnostic training built around real testing and real troubleshooting:
👉 Join Here – 14 Days for $1
scannerdanner.com/join-scannerdanner-premium.html
On ScannerDanner Premium, you'll get:
*In-depth classroom lectures based on the material in my book
*Case studies with real vehicles brought into class
*Troubleshooting using proven diagnostic methods
*Access to our private forum
*Fundamental training in automotive electrical, electronics, and drivability diagnostics
📘 Want to Learn More About Diagnostics?
Check out my field manual, Engine Performance Diagnostics, available as both an eBook and paperback at:
👉 https://linktr.ee/scannerdanner
ScannerDanner Tools:
https://linktr.ee/scannerdanner
⚠️ Disclaimer:
ScannerDanner LLC is not responsible for misuse, unauthorized changes, or incorrect application of any information provided. Always follow proper safety protocols when using tools, equipment, or procedures discussed in this video. Use this content at your own risk.
0:00 Intro
0:23 Reading the brake light wiring diagram
0:58 Testing the fuse with a test light
1:15 Finding a blown fuse
1:50 Fuses don’t blow for no reason
2:15 Replacing the fuse and testing brake lights
3:16 Inspecting the bike rack wiring
5:05 Tracing the brake light circuit
6:23 Narrowing down the shorted circuit
7:30 Testing the trailer harness wiring
8:12 Finding another blown fuse
9:31 We found the culprit
10:27 Brake lights work after unplugging module
10:36 Why the fuses blew
11:51 How the trailer module controls the lights
12:15 Final diagnosis: shorted trailer harness module
12:25 Bonus footage
![Chevy Corvette Cold Engine Misfire [Part 2]](https://i.ytimg.com/vi/lnG4Jl92TEw/mqdefault.jpg "Chevy Corvette Cold Engine Misfire [Part 2]
00:00 - review of fuel trim vs misfiring
00:48 - review of RPM drop test and driver shut-down
03:37 - review of spark plug color/cooling system
04:40 - review of secondary ignition waveforms
07:23 - lean misfire that I missed!
08:03 - internal vacuum leak (V-type engine)
10:20 - concerns of contaminated fuel/sticking injectors
11:07 - clip of unsticking an injector
11:55 - smoke test on the intake (vacuum leak test)
13:33 - picoscope secondary waveforms
16:47 - Snap-on vs Pico (zoom differences)
17:08 - SDP Scope and Scan Tool Classes https://www.scannerdanner.com/scannerdanner-premium-chapters/scope-and-scan-tool-classes.html
21:22 - setting a scope trigger
22:15 - flex-fuel Jeep review
https://youtu.be/glYGv3CyVWU (part 1)
https://youtu.be/Hjgs_8wX6Ks (part 2)
https://youtu.be/7kgnwJX40C4 (part 3)
23:50 - suspected sticking injectors (lean misfire waveforms)
25:04 - #2 cylinder lean misfire
25:37 - whats the fix?
28:25 - SD Premium!
https://www.scannerdanner.com/scannerdanner-premium-chapters.html
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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium https://www.scannerdanner.com/join-scannerdanner-premium.html There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.")
