I have never been aware of 24-volts anywhere in our Freightliner systems. I have seen other trucks (mostly military) that did. Even though we have two 12-volt starting batteries, they are wired in parallel still providing only 12-volts.
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Rob R.
Akron, OH
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST