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Next, check the voltage at the battery; it should be the same as the alternator output. If it is lower by more than 1/2 V, there’s resistance or a bad connection between the two. Here it’s shown that the voltage drop is about 0.2V drop, which is OK. With the new 100-amp plus alternators, an additional wire, 10 gauge or larger, between the alternator and the battery source (starter solenoid) is recommended. If turning off a specific item allows the voltmeter to return to its normal reading then that item is in need of a relay to allow current to be supplied directly from the battery source.