That's set by the "boost" adjustment. There are two adjustments. The maximum braking action is adjusted first by setting the maximum voltage the brake controller provides, using the manual lever. This is supposed to be set to produce incipient lockup during a sudden emergency stop. That way in a panic stop you get all possible braking action on all 3 axles. The problem is the travel trailers are pretty heavily loaded so often can't be made to lock up their brakes even at the max voltage setting. 

The other adjustment (Tekonsha calls it "boost") sets how aggressively the brake controller increases the voltage output based on the deceleration it senses the rig is undergoing. The higher the deceleration rate the more aggressively you're using the tow vehicle brakes so the more aggressively it activates the trailer brakes.  So it essentially creates the balance between your tow vehicle and trailer brakes. You can set this as you prefer, generally the heavier the trailer relative to the two vehicle, the higher you want to set the "boost". What I do is use my IR thermometer to adjust the boost setting so the trailer and tow vehicle brakes get roughly equally hot after descending a long grade (using mostly engine braking of course). 

Its hard to see what would cause the pin to be bad or the meter to be confused so that it gave a 3V reading when the wire connected directly to it gave a 12V reading. Were you using the same ground reference point in each case? Did you make a good connection to the pin when you tested it? 

What you need is an old school, incandescent 12v circuit test light. The kind with an actual (and clear) bulb in the handle, not the LED type. You can buy these at any auto parts store if you dont have one. This tester will put a small 'load' on the tow vehicle brake circuit.

Using the test light, test your battery to verify the tester is working, and to see how bright the light gets with 12-13 volts. 

At the rear of the vehicle, ground the lead and then probe the correct pin on the connector. It will be handy if you have a helper to operate the controller and press the brake pedal while you observe the test light.

The bulb brightness should vary from off, to dim, then to full brightness as the brake controller is modulated or the brake pedal is pressed.

Also, electric brakes tend to be a bit weak until they are 'burnished' in or 'settled' in. As stated by offgrid, they need to be operated several times at low speeds to get a feel for whether they are working. 

Then you need to either use an IR gun or the back of your hand and quickly feel the brake drums after a couple of stops. Both sides should be warm to hot, depending on how aggressive you are when braking.

If they are, you should be good to go. If one side is still cold, you have some more work to do.

I have a 2017 R-Pod 180.  Recently I repacked my wheel bearings and inspected my brakes.  I noticed that the 1 shoe on the drivers side was really worn.  I decided to replace the whole break assembly and hub.  Very easy replacement.  

After I got everything back together, I adjusted my brakes on both sides.  I adjusted them according to every youtube video I could watch.  I can spin the wheel on both sides, but hear a slight drag of the brakes.  

When I road tested it, I decided to set my brake controller (Prodigy IQ).  I quickly realized that my brakes were not doing much of anything.  I readjusted my brake controller.  I ended up cranking it all the way up.  As a result, I can feel the brakes working.  If I'm coasting at 20 MPH and hold my manual override button on the controller, I can just about make the truck and trailer stop.  I feel like they should be more powerful though.  If I crank up my brake controller, shouldn't I be able to just about lock up my trailer tires?  

We are leaving in 12 days for a 4,000 mile mountain vacation.  I really need to get this figured out!  

I've tried different combinations of brake adjustments and controller adjustments and seem to get the same results.  

Any advice?