Alternator overcharging??

[Alphasig112]

All my gauges go onto the low peg when key is off. Might try unplugging the cluster and see if that drops them to the pegs. If it does there are issues in the electrical system, if not cluster is bad which is not unheard of on an 06.

I will disconnect the batteries tomorrow and see what the gauge does.

 

[Alphasig112]

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Batteries disconnected. Gauge cluster is just reading wrong.

 

[NSperduto]

While ambient temperature will effect voltage charging rates, as a precaution, you might want to check the voltage of EACH battery with the truck running with a digital voltmeter, as it IS possible for the ECM to overcharge one battery or the other if the one of them is going bad or if the crossover cable is going bad (fairly common occurrence) or even if there is a posse or dirty connection on one of the battery terminal or engine ground points. Better safe then sorry, as overcharging can and will eventually cause battery failure. Battery voltages in a dual battery system should be nearly equal to each other when checked with the engine running, anything different is indicative of a problem developing.

I just had this exact thing on my '04 today. Gauge read fine, one battery charging 11.6 and the other charging 16.6. Cleaned up all the connections and the crossover cable. Both charging 14.4 now. Gauge still shows the same reading.