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Andy
Andy, Truck Diagnostic Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 1571
Experience:  International trucks, International, Maxxforce and Cummins engines, diagnostic, electrical, Hvac and refrigeration repairs
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The brake lights are working on my truck but not the

Customer Question

The brake lights are working on my truck but not the trailer. Pulled green cord out behind cab and tested stop light voltage and there is no voltage at back of cab
Submitted: 4 months ago.
Category: Medium and Heavy Trucks
Expert:  Andy replied 4 months ago.

Hi there . My name is Andy ! Can we start with the full vin number please ?

Customer: replied 4 months ago.
1fuja6cgx1lj13038
Expert:  Andy replied 4 months ago.

Here is a wiring diagram for your specific truck's light system

Customer: replied 4 months ago.
I would assume that based on that pic, the power goes from the pdm to the switch to the 7 way connector so I should check for power in the pdm and if there is power there but not at the switch it's between them. If it's at the switch but not at the 7 way it's between that run??
Expert:  Andy replied 4 months ago.

I would check right behind the 7 way connector for power on the brake terminal . It ma just be the plug itlself that has a bad or loose connection behind it .

Customer: replied 4 months ago.
I pulled the 7 way connector cord out and tested the out side of that plug behind the cab. Are you saying that I should check the in side of the connector behind the cab??
Expert:  Andy replied 4 months ago.

I would follow the wiring back from the trailer female plug mounted on the back of the cab to the next connection inline and test for brake power there .

Customer: replied 4 months ago.
Do you have any idea where that wire leads to?? The firewall??
Customer: replied 4 months ago.
Do you know where that brake light switch is located??
Customer: replied 4 months ago.
Does that look right for the brake light switch behind the cup holder and cig lighter??
Expert:  Andy replied 4 months ago.

I cannot tell from that image but there should be two switches ... one for each side of the air systems... one on primary side and one on secondary air side.

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