Turn signals and clearance on trailer not working

Guys

so in the Chicago area and winter with salt sucks. Truck was having issues where the right turn signal was staying on (not flashing) when the lights turned on then when you would turn all lights off and turn on the right turn signal both would flash L&R. The right one would flash by itself when turn on and 4 ways would work also. Now I have no turn signals at all running lights on or off. I have power at the fuse panel when checking with a test light. Also now I have no clearance lights on the trailer. My trailer has the 3 taillights on each side and 3 smaller marker lights in the middle. So the middle 3 marker lights are not working along with the outside clearance/turn signal lights as well. There is no power to that plug on my trailer pigtail. Problem is isolated to the truck but don’t know what it could be

any suggestions? Could it be the flasher relay? Turn signal lever/switch itself although not sure that would affect power to the trailer marker/clearance lights.
It’s driving me crazy please help if you can.
Thanks Nick

 

So you checked for power on all the pins of your 7 way? Using the top center pin for a ground, top two left and right are marker/tail, next two down left and right are turn, bottom center is brake lights.

What are checking power with? Test light?

 

Yes a test light. No power to the turn signals nor the marker. Twilights and brake lights show power. The issue is definitely at the tractor someplace.
I did find the little hose for the windshield washer sprayer is broke at the plastic piece the hose slides into on the drivers side so washer fluid was spraying inside the dash there when driver used it. Obviously he wasn’t aware of what was going on behind the dash

 

Have you checked at the back of the cab, where the light cord plugs in?

What truck is this?

 

I have. That’s fine. It’s a 2002 Peterbilt 379 day cab

 

Do those later 379's still have all the wiring come out of the firewall on the left side? Used to have a cover with three 3/8" screws

And when ypu say you checked it at the lback of the cab, you mean checked it for power?

 

Correct. The problem isn’t in the cord.

 

Don't blame the salt. Blame the hack that left connections open to the elements. Nobody can diagnose this issue over the internet.

Get out your test light and start checking grounds and continuity on the only wiring leading from the fuse box to the plug. That's not a common place to find an issue so it might be time for a new pigtail harness.

Check all the pins on the female receptacle in truck where the pigtail plugs into. If all is good then it's the pigtail harness or the female receptacle on the trailer.

 

Thank you Lamoverit but I’m looking for suggestion on where the issue may be. Ex… relay, fuse, flasher, etc. I’m sure I’m not the first one to deal with no turn signals on my tractor/trailer and market lights in trailer. It’s the first time I’ve encountered this problem.

 

Last time one I was pulling had a similar problem, it was melted wires at the back of the plug on the tractor.