Turn signal issue

[77 K20]

Normally I have time to poke around and fix things myself- but the wife's car is not working and waiting on parts to show up. So both of us are using my old truck right now... plus I'm working 12.5 hours shifts. I don't have "spare" time and hope someone can quickly narrow this down.

Neither left nor right turn signal works IF the brakes are being used. When signaling right/left with brakes on the front turn signals light up (on constant), the green turn indicator in the dash is on constant. The rear brake light does a quick flicker but is still on solid. (at normal "brake" brightness).

Other info:

-Turn signals work fine with no brakes on.
-Turn signals work fine with headlights on.
-Hazards work fine with no brakes on.
-Hazards with brakes? All front turn signals are on constant and both green turn indicators are on constantly in the dash. (but thought this was normal)
-I've owned the truck 10+ years and they worked until 2am this morning. It is raining/snowing/sleeting.
-I haven't changed any bulbs recently. All bulbs can light up.
-I have trailer wiring. I bought wiring that plugs into the connector behind the rear bumper (9 years ago). I sealed the connectors in black RTV to keep the weather out. Connector still looks great and looks to be sealed.
-I know all grounds on the engine/firewall/frame/radiator support are clean, ground down to bare metal, star washers used, then sealed on top with RTV/liquid electrical tape. Additional massive ground wire from the battery directly to the frame.

My guesses right now would be to replace the flasher unit. It is 7 years old. Next take apart the rear taillights and look at the sockets. Unsure where the ground is for the sockets.
Then maybe the turn signal switch in the column? Don't own a steering wheel puller and hate messing around in the column.

Is my thinking wrong here?

 

[Georgeb]

You said both fronts iluminate solid with he hazards. Do both fronts iluminate for either left or right turn or only the side selected by the turn signal switch.

 

[77 K20]

You said both fronts iluminate solid with he hazards. Do both fronts iluminate for either left or right turn or only the side selected by the turn signal switch.

Only the left front will illuminate when signaling left. And the right front will illuminate when signaling right.

The wife sent a text when she got to work. Said the first time she signaled with the brakes on it actually worked for about 10 seconds. Then the turn signal was "stuck" on.

Then was not working the rest of her drive.

 

[Oldrider]

On my 85, the green signal being on and not blinking with the blinker means I have a bulb out. Not sure if this helps.

 

[77 K20]

It has something to do with my trailer wiring. When I got home this morning I crawled under the truck that dripped all over me (rain snow mix while driving).
I bought a T fitting years ago to tie into the factory light harness and then sealed it with black RTV. Cut the RTV and removed the T fitting (so bypass trailing wiring). Turn signals work again.
So in the spring when the weather is nicer I'll go thru all the wiring and figure out what happened. I have a 6 pin trailer plug in the bumper and a 7 pin in the bed for the 5th wheel.
I hate trailer wiring. Spent a ton of time on it when I first did it to make sure I didn't ever have to mess with it again. I was wrong.

 

[1987 GMC Jimmy]

This probably happens to everyone who has a truck and a dog, but we used to have a golden retriever about thirteen years ago that chewed through all the trailer wiring at the rear of my dad's truck. You said you hate wiring so if you have a dog, especially a young one, don't let them near the underbelly of the truck. Just a little anecdotal $.02.