They usually relied on socket to housing to brackets to body to frame for ground. All "touching/fastened" to each other. You can see the multipath problem of getting back to the neg battery terminal. That's why it's usually the ground. But I always start with making sure I have power first to the bulb contacts. Run, stop and blink power. The ice pick tester bulb will operate just like the real bulb...run, stop and blink. (if you have an absolutely sure test ground)If the power does not work with a good test ground, you work on the power distribution until you find it. If the test bulb works you redo/fix/add the ground path until it works. Again I say check the schematic from harness and schematic from Turn signal kit to understand the wiring. If you want to keep guessing theories you are wasting time. You need to buy a ice pick tester, take off the lenses, pull out the bulbs and test the socket in various modes.
