I have been trying to figure out the circuit that controls this universal power antenna's, three-wire (signal, power, ground), 12V DC motor:

Numerous folks have bench tested this power antenna and found the following:
Connect +12V DC to both the red and green wire and the ground to the black wire => the universal antenna extends fully.

Connect +12V DC to the red wire and the ground to the black wire => the universal antenna retracts fully.

Here is my best guess of the wiring, with switches shown in the position when the antenna is rising:


The biggest question I have is: How likely is it that these universal power antenna assemblies have an [edit: electromechanical] relay (like that indicated by the coil and DPDT switch in my drawing)?

 

Something like this! ?
Analog relay??

 

Analog relay??

Right, my bad. I meant "electromechanical relay."

Thank you for the great drawing.

 

I have seen those antennas with a up/down toggle switch, DPDT reversing arrangement. I have also seen them with a single 12 volt relay that is energized by the "antenna control" wire from the radio. That wire is open circuit with the radio off and +12 volts with it on. So the antenna system must have switches that stop it when it is full up or full down.
So the circuit shown in post #1 is the same as my guess as to how it works. Of course,How else could it work????
Take the power from the car's Accessory circuit, and be totally certain to have a correctly sized fuse in the feed,

 

So the circuit shown in post #1 is the same as my guess as to how it works.

Good to read.

Of course,How else could it work????

Assuming no solid state components or maybe some kind of mechanical clutch(?) are used in the universal power antenna, this (the relay coil operating a DPDT switch) is where I landed, too. I do not normally do circuit design (obviously) so this took a lot of thought for me. I posted to get some reinforcement on my student's understanding.

For the archives, why this arose: Certain Toyota models from the 1990s came with a Solid State Relay (SSR) design to operate their power antennas. From a 1994 Toyota Camry service manual:


The Toyota OEM power antennas fail from time to time. Folks are trying out aftermarket replacements but have generally not understood the differences between the Toyota OEM design and the aftermarket designs.

The universal power antennas do not get the greatest reviews. Maybe this is because any electromechanical relay cannot endure the wear and tear that an SSR can. Or the parts used in the universal's gearing et cetera are cheaply made?

Fuses for the universal power antenna substitution are in place in the Toyota OEM wire harness.

Just a little while ago I happened on discussion of a 1978 Chevy Monte Carlo's power antenna wiring at https://www.the12volt.com/installbay/forum_posts.asp?tid=145693. From the latter:


If a moderator wants to move this to the Automotive Electronics section at https://forum.allaboutcircuits.com/forums/automotive-electronics/, then I would appreciate it.

MaxHeadRoom and MrBill2, thank you for taking the time to instruct.

 

The Chevy circuit shown last in post #5 is the same functionally as the one I was going to suggest, which I have seen an automotive style relay made to do exactly that. The really good news is that exactly the same function can be provided with a better quality industrial rated DPDT 12 VOLT dc RELAY in a sealed housing, which will probably outlast the car. It does, however, place the demand for stopping the motor on the two limit switches that are part of the antenna assembly.