So if there is no 24v between the master and the CB, your master switch is open! What is the voltage at the Jumper Lug?

If there is 24v at the lug that means there's 24v at the master switch.
If you don't have 24v coming out of the master to the CB, bad Master.

If you have 12.8 at the lug, you have some serious battery cable issues and the paralel/series hookup is suspect.

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