Hi
@gglockner ,
I would make a recommendation.
Please do not roast the recommender...
Purchase a hard wired trailer brake controller..
I like Prodigy P3 - Roughly $150
I think you said you had or were ordering the 4 wire
trailer brake harness for Tesla - Sorry I do not have the part number...
Instructions for installing the 4 wire harness:
One wire is common - Negative
Second wire is 20 Amp Positive
Third wire takes signal FROM Tesla brake light
Fourth wire supplies Pin 4 Brake Controller output in 7 Pin.
Wire per these instructions and you will have functioning trailer brakes...
Without the above steps Pin 4 in the 7 Pin does NOTHING.
When you touch the brakes - the controller takes the brake light input
(modified by your setting of the inertial switch.) and supplies
a variable amount of voltage and current to pin 4 of 7.
At this time...
You will NOT have a Hot or Positive Pin 2 in the 7 pin harness.
I have simple instructions for making Pin 2 "Hot."
Disconnect the 7 pin receptacle from the car which will entail
Disconnecting a large Molex connector...
There are positions for 4 heavy gauge wires in the corners of the
connectors - 3 corners from the car have wires populated and the
4 th is empty and plugged.
When you match the plug from the car and the plug to the 7 pin
you will see 2 of the wires mate with each other. The third wire
is at the diagonal corner from the other wire - They do NOT match
hence no power to pin 2.
We found that the easiest way to make pin 2 hot was to move the wire
in the plug to the 7 way to the diagonal corner.
Now the wires mate and there is power to pin 2...
Please look at the connector below to visualize the work...
View attachment 790798
The tiny pins in the central rows are for lights - brake, turn, and reverse.
The heavy conductors are on the corners for Positive, Negative, and Brakes.
Good luck,
Shawn