Hi While underway I noticed both volt gauges reading around 12v on helm. On DC switch panel both reading charging at 13 plus as you would expect. When back home tested at batteries with engines running and confirmed charging at 13.6 volts so alternators appear charging ok. Found on port engine alternator small red wire coming from alternator had broken at female connector. Thought may have been issue. Replaced with new connector, started up again but no difference. Gauges start off showing around 10 volts then slowly improve to around 12.2 volts but no more. Again check at batteries and all charging around 13.6 plus. Couple of things, 1. what is the small red wire coming from front of alternator that connects through a female/male connector? Removed 4 x bolts from cover from front of alternator to see where it goes to and it gets embedded into the cover. Would this wire have anything to do with gauge reading? 2. I presume both engines have totally independent charging systems, i.e each alternator independently charge each battery system. Question being, if problem was restricted to one side only, why would both gauges both report similar voltage? On our way out both were reading as they should, up in the 13.6 plus range. Then on returning both down to around 12 on the port and 12.2 on the starboard (stbd always reported slightly higher). Worth noting that I did notice recently both volt gauges slightly flickering (pulsating) when underway. Could fault be at gauge, in this case both gauges giving up at same time?? Currently in process of replacing both tach’s as reading all over the place. Any help would be greatly appreciated. Thank you.