[Deadhead]

Most likely the ground is screwed up between the parking lamps/bulbs and the body. Test by running a known good ground to them. You may have to scratch and scrape on the housing etc. to get good contact. That may not reveal the issue. You also will need to push on the bulb while the signal is actuated. Also try jamming some Alum. foil down in between the bulb and the housing. Try all kinds of pushing and twisting of the socket and crimp where it meets the white housing. I have had this issue before. Pretty sure I ended up with Alum. foil jammed in my current driver bulb. Been working for over a year since I had a similar type issue. I was actually able to get mine to work out of the bumper and then when put back in it would not function right. Had to take it in and out a half dozen times to get a permanent fix. Do not ask me how you get it in and out. You will just have to turn it until it slides out. Like a Rubick's Cube.

Check wires and connectors to the lights as well. This might not be it, but I'm pretty sure you will find the Prob. in the front lamps/housing. Pretty much forget about finding another in good shape. If yours is not badly rusted, I would work with it to make it work.

Another thing to look at is where the wires pass through the steering column. Non-tilt column shift cars will often have a short or broken wire where the ribbon passes through the metal.