SCL comes first

The third pin is the clock

Left to right with the parts facing you: GND, 3V3, SCL, SDA. Most I²C boards, including the TK31 EEPROM and the INA3221, print SDA before SCL. A row of jumpers moved from one of those to this block swaps the two lines.

Nothing is damaged when that happens. The chip simply never recognises its address, so a scan finds nothing and the sketch reports no INA219 — which looks exactly like a dead board. Read the silkscreen, not the wire colours.

The 3V3 hole sets the bus

The hole is printed 3V3, and it is the chip's own supply, which may be anything from 3 to 5.5 V. The block's two 10 kΩ pull-ups run from SCL and SDA to that same hole, so whatever you feed it is the voltage the two lines rest at.

That makes the rule simple: feed 3V3 from your board's logic rail. 3.3 V on an ESP32 or a Pico, 5 V on an Uno. The chip treats a line as high from 0.7 times its own supply, so a matched feed always leaves a clear margin.

The two ways to get it wrong both come from the pull-ups. 5 V on the hole beside an ESP32 puts 5 V on two of its pins. 3.3 V on the hole beside an Uno fights the Uno's own weak pull-ups to 5 V and lifts the clock above the chip's limit.

Finding it

A scan is the quickest check that the wiring is right. With nothing soldered on the back, the block answers at 0x40.

#include <Wire.h>

void setup() {
  Serial.begin(115200);
  delay(500);
  Wire.begin(8, 9);  // ESP32-S3: SDA 8, SCL 9
  for (uint8_t a = 1; a < 127; a++) {
    Wire.beginTransmission(a);
    if (Wire.endTransmission() == 0) Serial.printf("found 0x%02X\n", a);
  }
}

void loop() {}