Service Home Mechanical Limit Switch - Troubleshooting Guide - TG0098
Last updated: 10/14/2025

Mechanical Limit Switch - Troubleshooting Guide

TG0098

Introduction

Mechanical limit switches have two configurations:

  • 2-wire that have (1) NO circuit.
  • 4-wire that have (1) NO circuit and (1) NC circuit.

Mechanical Limit Switch Wire Color Code Table

Configuration Wire Color Switch Type
2-Wire Blue/Brown Normally Open
4-Wire Black/Black Normally Closed
Blue/Brown Normally Open

Symptom Table

Symptom Possible Cause Corrective Action
The plunger sticks or moves slowly. There is contamination on the plunger. Make sure the plunger is clean.
The diagnostic bit does not change state. The switch has stuck contacts. Measure the resistance on the switch.

Contacts

Corrective Action:

  1. Use the Mechanical Limit Switch Color Code table to determine which pins are used for NO or NC contacts.
  2. Set your multimeter to measure the resistance. Place the probe tips on the correct pins for testing. Open contacts should measure about 100 kOhms. Closed contacts should measure 0-3 Ohms and should never measure higher.
  3. Repeatedly activate the switch and verify that the switch changes state each time. If there is no resistance, or if the resistance is too high, replace the switch.
  4. Connect the switch to the control cable and repeatedly activate the switch. Check the input bit on the diagnostics screen to make sure that the bit changes state each time.
  5. If the bit does not change state, the connection is loose or the cable is damaged. If you suspect contamination or damage, replace the switch.

Contamination

Corrective Action:

If the plunger sticks, clean the roller assembly on the switch. Make sure the wheel and the plunger [1] operate correctly.