Learning Smart Ballast Diagnostic LED Indicators

Lights seem so simple. You flip a switch, and they turn on. The trick is to make things nearly that simple when the light doesn't turn on. Enter the Smart Ballast. On most MCI coaches, aisles are illuminated by fluorescent lights, which are, in turn, energized by ballasts.  Unlike normal ballasts, a 'smart' ballast incorporates an LED diagnostic system to help determine why the light is not lighting up. When the ballast and fluorescent light are energized and working properly, only the green LED will be lit.

If ever an aisle light fails to illuminate, these troubleshooting tips should help you determine which component of the fixture has failed.

If there is a fault in the ballast, fluorescent lamp or the wiring, the red or the red and green LED will light up. If both the red and green LED are lit up on the ballast, check the lamp fixture for the following failures or events:

  • Open Circuit Protection

    When a lamp is removed, the ballast shuts down.

  • Lamp End-of-Life Indicator

    When a lamp failure is detected, the ballast shuts down.

  • Arcing Protection

    When arcing occurs from the output leads to the ground (vehicle body), the ballast shuts down.

  • Ground Fault Protection

    If a person accidentally takes an electrical shock from the ballast output leads or lamp sockets to the ground (vehicle body), the ballast shuts down.

When the fault is repaired, the red LED will turn off, and the ballast will restart once the coach battery-disconnect switch is cycled.

If the red LED is lit up by itself, check the lamp fixture for the following failures or events:

  • Reverse Polarity Protection

    When the ballast is connected in reverse polarity, the ballast does not work but is energized.

  • Over-Temp Protection.

    If the ballast temperature is too high (over 105°C or 247°F), the ballast turns off.

  • Overcharge and High Voltage Transient Protection.

    If the ballast stops working due to a high voltage surge or overload, restart or reset the ballast by cycling the main battery-disconnect switch. However, if the red LED turns on and the green LED turns off a second time following the ballast reset, you must replace the ballast.

In the end, it is indeed pretty simple — and with a parts list to match. For your convenience, here are the numbers of the aisle-light fixture parts you may need:

Fluorescent Tube (03-08-1031)
Smart Ballast (07-08-2541)

For more information, see Section 7 of the MCI Maintenance Manual or call Technical Support at 800-241-2947. And may all of your travels be bright.

The FYI from MCI editorial staff values your feedback. Please e-mail any suggestions, comments, or ideas for future articles to

Motor Coach Industries - An NFI Group Inc Company: Corporate Address 200 East Oakton Street, Des Plaines, Illinois 60018 | Phone: 866-MCICOACH

Copyright 2004-2018 Motor Coach Industries Int'l, Inc. and its subsidiaries. All Rights Reserved.