Brake light not working one side only - Diesel Forum - TheDieselStop.com
7.3L IDI Diesels (Not Power Strokes) Technical discussion of topics related to vehicles powered by the 7.3 Liter In-Direct Injection Navistar engines.

 
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post #1 of 3 (permalink) Old 09-15-2018, 07:58 PM Thread Starter
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Brake light not working one side only

Driverís side brake light has quit working and it is not the bulb and not a bad contact. Is there a separate circuit for the left and right sides power to the brake light coming off the brake pedal switch? Maybe a loose connection on that side? I see they both run off the same fuse so that is not the problem.

Thanks you.
Rich

1993 7.3 IDI F-350

Former USCG diesel mechanic. Procedures described here are not for everyone. Your results may vary. Side effects may include tissue damage. Check with your doctor.
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post #2 of 3 (permalink) Old 09-15-2018, 10:02 PM
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Quote:
Originally Posted by ob99email View Post
...not a bad contact.
How do you know?
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Originally Posted by ob99email View Post
Is there a separate circuit for the left and right sides power to the brake light coming off the brake pedal switch?
No, but there is at the MFS. Click this & read the caption:


(phone app link)


You can find your truck's wiring at this link:
BBB Industries- Premium Alternators, Starters, Power Steering Products | TSB's & Wiring Diagrams
It requires an e-mail, but it doesn't check that it's yours or even real.


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post #3 of 3 (permalink) Old 09-16-2018, 08:35 AM Thread Starter
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Break light not working one side only RESOLVED

Steve83, thank you very much!

This info was exactly what I needed since I didnít realize that the MFS controlled the brake light. Here is what happened:

Iíd been testing my brake lights without the power on as I often do when I hook up a trailer. (I test the turn signals first with power then the rest without power.) I didnít realize that the left turn signal switch was engaged and had caused a bypass of the brake light circuit on that side (as designed). After your reply, I was able to do a root cause analysis knowing what the MFS does and asked myself if I had maybe done the above. Tried it and found that is exactly what happened. Brake light is good. Thanks again.

Rich

Former USCG diesel mechanic. Procedures described here are not for everyone. Your results may vary. Side effects may include tissue damage. Check with your doctor.
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