Need assistance.. Electrical issues 2007 Volvo VNL

Any play in pigtail in other trailers?
I’ve got shim mine.
I’ve just got a zip tie I’ve folded/doubled and put it in bottom and tightens up the fit, or my lights will dim on trailer sometimes

 

In the wild seems the key. As your driving around, components and wiring harness are vibrating. I dont understand what jumping the 7 pin means, i'm assuming it's somehow completing the circuit and therein lies the biggest issue with electrical faults. Hunting down where.

It's really hard to say, i'm not super familiar with an LCM but am guessing its like any other analog controller. The faults they throw can mimic wiring/harness issues. If you can isolate the LCM try smacking it around wired while observing the expected light function.

Hey i got real lucky on a Stanley Automatic door opener once and did just that. There is sadly no way to test many of these specialized controllers out of part swapping and it gets expensive quickly!

 

I would remove the set screws on the tractor trailer pigtail, trailer end, and push that plug into the trailer receptical with a screw driver. Then check voltage at that wire connector when the lights are not working. You know the red one at he bottom.
If that is bad then check the other end of the cord the same way. Then what is next easiest? Same check on pigtail plug on the tractor side plug or where the harness goes the the firewall?
Doubt it is the brake light switch as there are two of them. Catching myself in possible error.
Do the brake lights fail on the tractor and the trailer?

 

Start at the battery terminals. Make sure all the connections are clean and tight. Do you have a battery disconnect switch? if so make sure all the connections on it are clean and tight. There is a power and ground cable that connect to the pass through panel on the firewall that supply power to the cab. Are the connections clean and tight inside and outside? The trailer cord has a male plug on both ends one end plugs into the trailer the other plugs into a plug on the truck, is the truck end plug clean and corrosion free? check there with a test light for brake light power. Check the simple things first.

 

it sounds like the problem is with your truck.. most likely a wire has come loose or corroded off on the truck side of the plug... if the cord is brand new then maybe those screws that hold the wires onto the plug is loose.. why the hell these shops want you to throw computer modules at #### without troubleshooting with basic electrical troubleshooting skills is what is wrong with these dum dums.. start at the plugs and work back towards the engine bay.. sometimes a wire is rubbed thru behind stuff underneath the frame where you cant quite see it.. you are going to get dirty but you got to follow that electrical cable every inch of it , if the problem is not the plugs... im willing to bet the cord is either rubbed thru somewhere under the frame or the problem is in the plugs.