Trailer Stop Lights

[Clifford the big red dog]

okay guys and gals,

I have a 2014 mack cxu with the mp8 engine, auto trans. here's my problem:

*light switch ON either park lights or headlights both, tap the brake and trailer stop lamps come on. after releasing brake or trolley lights stay on and relay is not resetting.

*light switch OFF all trailer braking lights function normally. 

*when the switch is on I can turn on flashers and brake lights for trailer function properly.

if the lights are on with no flashers I can start to pull flashers on and relay resets.

tractor stop lights work as they should, its strictly on wires to trailer pigtail/

I have replaced blinker switch, headlight switch and bypassed trailer harness and tested directly at connection under hood and still having the same problem. any help would be greatly appreciated thank in advance. 

 

 

 

 

[Joey Mack]

take the trailer cord plugs apart and look for a loose wire or frayed wire ends that have reached over and crossed up with another... or....  find a known good cord from another truck and swap it to see if its still an issue... jojo

[Joey Mack]

pull the socket out of the trailer and look for the same thing there... they shake loose and this happens...   jojo

[Clifford the big red dog]

joey mack I will definitely check that out tomorrow. 

I did remove the red wire from the block on the firewall and tested the connection it goes to with the same results.

 

 

[Joey Mack]

start simple first...  My guess is a loose/crossed wire... it only takes 1 strand of wire to 'F' it up... jojo

[Clifford the big red dog]

I totally agree, I think tomorrow I will remove the wires going back to the pigtail from the firewall and test again.

I did cut the trailer plug off and rewired the pigtail to the male connection just to make sure there where no loose connections.