Reverse polarity / voltage reducer

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Joined Oct 15, 2005
1) In a 12VDC mulit-load (parallel circuits supplying CB, Car Stereo, fan, lamp, aux power outlet, etc.) set up supplied by one power supply (truck battery), how do I determine the correct size diode reverse biased to install across the main DC power source and what sized fuse/circuit breaker would need to be installed in order to pass the highest current normally drawn but small enough to blow if reverse polarity were to happen?

2) When installing a Signal-Powered volt meter with an LED backlight on a 12VDC power supply, the instructions say to "add a series resistor R if the backlighting supply voltage is higher than 5 VDC". How do I determine the correct resistor? Are these type resistors identified in some other way? Allied Electronics doesn't list "Series R" resistors in their catalog.