This has been done using a signal switch from Speedway and an Advanced Turn Signal Module from Signal Dynamics
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I have a fully functional self cancelling turn signal in my Model A using an after market stalk mounted unit.
I first disassembled the turn signal unit and unsoldered all wires from the board except the yellow, green and black. I then cut the yellow, green and black at about 18", this is dependent on where you will mount the control module. I then cut all the wires to reach the control module location. I installed female bullet connectors on the 9 wires coming out of the control module and male bullet connectors on the yellow and green wires coming from the switch and all the wires that were cut back to reach the control module.
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As you can see in the picture above, I ground the detents from the actuator arm to make this a momentary switch. The arm after depression, automatically returns to home position. If you tap the arm to full extent and immediately let it return, the signal will flash for 7 seconds, holding the arm in signal position for 2-4 seconds gives you a 20 second signal and pressing over 4 seconds gives you a 75 second signal, When the signal is flashing, hitting the signal arm one more time will cancel the signal, especially good on the 75 second signal.
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The color coding on most turn signals is the same so it doesn't really matter whose turn signal unit you use.
Here is a schematic built around the Advanced Turn Signal Module from Signal Dynamics
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The module can be ordered online from Signal Dynamics for about $120. There are other units available from them, but this one seemed to cover all the bases. You will not have 4 way flashers with this install. These units are primarily manufactured for use on motorcycles using two momentary switches. This seems like a lot of talk, but it is a fairly straight forward install. Let me know if I need to do any edits. Hopefully no more on going signals frustrating other motorists.
Warren
To see pictures related to this post, go here. Sorry I had problems posting pictures.
https://www.jalopyjournal.com/forum/threads/turn-signals.1310617/ post 43