Turn signal and headlights

Hi all. I'm starting to work through my 70 Torino Brougham and would like to get it to the point where I can safety it. Ontario Canada standards are fairly rigid. I have most of the items squared away but I am tackling an electrical problem that I can't narrow down.
All the lights work incl: turn, headlights, tail license plate, markers etc...but when I turn the headlights on, my left side markers have about half the voltage that the right side does and the front left running light is also very dull. When I turn the left turn signals on...nothing. Turn the right on, no issues. The left turn signal on the dash remains on from the moment I turn the headlights on, regardless of turn signal position.
I first thought of it as a ground issue. I checked the grounds in the trunk but I can't find any up front to check. Are there any?
After that I tried to see if it was a short between the markers and turn signals but I can't find anything. The only wiring I have not checked is under the dash.
Could this be a relay or turn signal switch issue or are there grounds I'm overlooking.
Help would be appreciated.
I don't think it matters, but the turn signal bulbs on the front are led bulbs as well as the back. I don't think that is the problem because the right side works fine headlights on or off, whereas the left side just doesn't want to cooperate with the headlights on.
Thanks again.

Thanks for that. I've spent a few hours trying find the grounds up front. Nothing. The electrical diagram indicates there should be something but I can't find anything. The wiring harness looks original and I havnt found evidence of wiring mutilation...Well on the front end anyways.

Thanks for that link. That is the wiring diagram I have been using. I disconnected the turn signal socket from the main harness and am only getting about 4-5v at the connection with the headlights on. So it almost seems like something else in the system is causing low v9ltage to the turn signal and left markers. I'm not a wiring or electrical person at all so I could be wrong in my approach.

yes they are usually coming right off of the headlight connector, should be something similar at the tail lights too
4-5 volts? sounds like a corroded connection somewhere???  if it's been sitting a long time try working the switch off and on a bunch of times to scrape a clean connection!  could be the switch is bad...

Thanks all. I've replaced all the marker lights and was able to get all turn signals and markers to work how they should when using the hazard lights with the headlights on...but the left turns still dont want to work as they should with the headlights on. I've gone through the front end with a fine tooth comb and havnt found any grounds. If anybody has a pic of their grounds on a 70/71 model I'd appreciate it. I will probably order a couple flasher relays tonight and the front turn signal sockets as they are starting to look a little rough. Pending the ground situation my next thought is the turn signal switch which I havnt touched yet at all. I tried to clean up all the connections too.

Good news. It's all sorted. It ended up being the little led bulbs in the front turns. As soon as I replaced those everything worked like a charm. On another note, I still can't find any grounds from my headlight pig tails. I'm assuming something must have been done at at some point to change the original setup. Basically every front light wire disappears into an electrical tape wrapped wiring harness with the only black lead protruding to the surge protector box near the starter coil. I've spent hours trying to find the grounds and short of removing the current harness, I lost the battle. Either way, problem solved for the time being but it would still be nice to see what OE looks like for reference.

that's wild