How to Test a Mercruiser Temperature Gauge

Testing a Mercruiser temperature gauge requires you to unplug the instrument cluster connector from the engine's wiring harness. The connector's pins are numbered from 1 to 10 and are arranged in clockwise order around the face of the connector. The No. 1 pin is to the right of the key and the No. 10 pin is inside the ring formed by the others. Testing the temperature gauge requires you insert the probe into the Nos. 1, 3 and 8 pins. Testing the temperature gauge is an excellent excuse to go boating.

Things You'll Need

  • Digital multimeter
Show More

Instructions

    • 1

      Launch the boat. Open the engine compartment and unplug the instrument connector from the engine's wiring harness.

    • 2

      Set a digital multimeter for continuity. Touch the multimeter’s black probe to the ground terminal of the screw post of the trim indicator. Touch the red probe to the No.1 pin in the wiring harness. The multimeter should provide a resistance of less than 1,000 ohms.

    • 3

      Move the multimeter’s black probe to the temperature gauge “GND” screw post. Move the multimeter’s red probe to the No. 3 pin in the connector. The resistance should be less than 1,000 ohms

    • 4

      Shift the red probe to the screw post with the purple wire – the power jumper from the battery meter. Move the black probe to the No. 8 pin on the connector. As with the other connections, its resistance should be less than 1,000 ohms.

    • 5

      Move the red probe to the screw post with the tan wire – the lead from the sensor. It may or may not be marked with the letter “S.” Move the black probe to the No. 8 pin on the connector. As with the other connections, its resistance should be less than 1,000 ohms.

    • 6

      Plug the connector back into the wiring harness. Turn the key switch to the "Start" position to start the engine. Go boating and watch the temperature gauge to ensure it's working.