By Purkeys | Jul 13, 2015

TMC’s RP-137b sets the industry standard for voltage drop on the 7-way connection. When voltage drop is measured on the 7-way, three circuits are tested. The common ground, the AUX pin and the stop lamp circuit are tested under load to determine if adequate power will be available at the front of the trailer.

Purkeys Sales and Service Engineer Larry Rambeaux demonstrates how to use the chart in RP137 to determine if everything is working properly. The chart in RP-137 compares voltage and current. This means that as the current increases, so does the voltage drop while the resistance stays constant. According to Larry, “You’re simply going to look at what the load is and go up the line to determine what the voltage should be.” If the measurements for the amperage and the voltage meet on the chart above the line, the 7-way passes.

If the measurements don’t correlate with the “pass” section of the RP137 chart, the ABS may not work properly. When this system isn’t adequately powered, fleets can experience safety issues and minimized tire life.

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