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School Bus Turn Signal Wiring Troubleshooting

I got a call this morning from one of our drivers who said he had no right hand signal light. Most times it’s a basic repair but then again this bus has LED lights. LED are the best lights to have simply because they rarely fail. There’s much better illumination and according to the motor vehicle inspection manual they can have a 30% burn out and still be legal.

So back to the story…..the turn signal lights on the right side were out completely. This was not going to be a simple fix so I had to issue a spare bus to the driver. As I’ve said in previous blog posts when attempting to troubleshoot electrical systems you absolutely must have a wiring schematic. Without one it’s like driving in a strange country without a road map. It’s anyone’s guess where to go next.

Of course the basics are still a good place to start with battery voltage and ground checks along with visual inspections of connectors and wiring. The first thing is digging up the schematics for this circuit so we have a place to start. The battery voltage feed is the first step to take which in this case will be a fuse that sends amperage through the flasher.

From the flasher the circuit goes to the turn signal switch then to the circuit board #4 under the right hand side of the dash. From there wiring runs to circuit board #1 behind the side panel door on the driver’s side. From circuit board #1 it feeds the right hand signal light. We checked the continuity and voltage readings and found a voltage drop with a reading of 5 volts.

At this point we are tracing through the right hand signal wire to find a frayed wire or bad connection. When we find the fault I will update this post. It’s much more enjoyable with electrical problems when you have the tools to test wiring circuits using the proper wiring schematics. We have a shop tool which can be probed into a circuit to check for continuity. It’s hooked to the battery positive and ground terminals so both a hot circuit and ground can be checked out.