Based on the description FMCSA 393.43, it is technically a violation, not to have the trailer air supply "clearly indicated" on the manually controlled device. Not having a label on the red knob, for the trailer air supply, could easily be justified as a violation. While this is often overlooked by inspectors, I encourage you to take the extra step and avoid the chance of a violation. And while you're at it, do it for your parking break too. #truckdriver #trucking #truckingbusiness #truckerlife

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