Blue Wire from truck to trailer in light cord always hot

You got it Brother. Glad it worked out. Sometimes just cleaning does not work. $700 Sam chassis and has to be programmed at Freightliner while installed on truck!

 

You betcha...anything else--just holler.

 

On my truck the center pin is always hot because of trailer tracking. Not sure if that was done to your truck.

 

This might be very easy fix. Trailer power relay must have 4 prongs (legs) if it has 5 then trailer will keep getting the power even if key is off position. If you have 5 prongs on the trailerpower , You can break the middle prong and try .

 

So is the truck designed to have constant power through the blue wire? I’m having the same issue with a truck. The trailer will not do self test due to having constant power. Pulled the trailer power relay and found that someone had cut off the prong of the relay on post 85. Put a good 5 prong relay in and still have the same issue. Am I chasing a problem that’s supposed to set up that way from the factory or do I have an issue? The reason this came up was because I did an annual inspection on the truck and found that the ABS light on the trailer was not cycling like it normally should during a self test after the ignition is turned on.

 

You have 7 wires to your trailer. Most common trailer issues, 7way connector short inside(corrosion) pins for 7way connector corroded etc. (#### gets in there and causes tons of electrical issues.) Aux, marker, turn signal(2) stop, power and ground( trailer abs) . Your wires are probably blue white black brown red yellow and green. I dont remember off hand which is which. But i can tell you that the blue and white are like 10 awg-12awg wires and the others 14-16.

 

Rdorsey28, For your constant power on trailer abs circuit. You need to check your R8 relay on the SAM Chassis. Your should have a 4 pin relay in there is you want abs power on with key on only. If you put a 5 pin relay the power on the ABS circuit will be always on.
Per SAM PIN layout wall chart " Pin 87 or pin 87a will be missing depending on the functionality of the circuit. If prong 87a is missing the circuit will be normally open, the trailer power circuit is enabled only if the key is in the IGN position or enabled through a switch (depending on SAM parameterization). If prong 87 is missing, the circuit is normally closed (BAT). If a 5 prong relay is used, the trailer power will always be on." Please try a 4 pin relay and update the forum with your results so all can learn.

 

Rdorsey28, Rocketyman back in his August 31, 2017 post explained this and actually posted a picture of part of the wall chart with the explanation of R8 relay in your SAM CHASSIS. So please look back on the thread, I missed that it had been posted earlier.