Need assistance.. Electrical issues 2007 Volvo VNL

100% of those things have been checked... Not only are most of them clean and corrosion free..... Lots of it is brand new...

 

That is what we checked yesterday. The cords and plugs are fine.... Or at least appear to be...
Not old... Not damaged... Not worn through....and this is a brand new 7 way cord on the tractor but I was happening with the old one.... Just replaced it 2? Days ago...

And they have checked twice and can't find anything wrong as the trailer lights at the shop light up just fine and the tests all pass.
I was told and it makes sense to me.... Can't find a broken wire for the trailer lights if the trailer lights are lighting up....
It was happening with the old 7 way cord too... I replaced it a few days ago because I had a small cut into one of my airlines and we got 2 oos recently on other trucks for similar reasons.

And I have zero electrical troubleshooting skills... I'm terrible with electrical.. I'd imagine I'd have an easier time with solid fuel rocket propulsion physics than I can figure out anything electrical....for some reason it's always been my kryptonite...

 

And as I mentioned at the shop... The 7 way test light all lights up fine...
The first 2 times I mentioned there was an issue they told me it was just bad chassis... Which I could normally believe because they are trash most of the time...
But when I check 7 in a row and they are all bad and about 20 over 3 days? Nope... Statistically impossible.

And when I saw the spotter moving mine and it worked for him that was good enough confirmation for me..

 

I should also have mentioned I guess that electrical is by far my worst subject..

If I am able to get that pigtail apart to check for voltage.... How do I do that? Red on red and black on the ground of the pigtail?
Red on red and black on the chassis frame?

 

Yes. At the shop they are saying everything looks good.

The 7 way cord from the back of the cab to the trailers is 3 days old... The one under the cab is maybe 2 years.

Took all connections apart and looked for signs of corrosion and there was none.. A few years back when I replaced the one under the cab I did the same thing I do for every single electric component I replace and that is slathering the connections with electric grease to keep out moisture and corrosion and such.

They used the 7 way tester that plugs into the cord and everything lit up properly.

Someone brought an empty Schneider back to the yard last night... I just hooked up to it... Everything works fine..

I'm just doing the bungee on the hand brake to check but all lights work as they should...

I just replaced the 2 sensors on the pass thru near the clutch because the eld is giving me errors for both sensors... Hoping those go away... Maybe it's related because they are specifically for brake lights but I'm told it probably won't fix anything.


And no... Changing those sensors didn't even stop the error codes from popping up..... Great...