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Volt Gauges Reading 12 Volts

Discussion in 'Electronics Q&A' started by Tantalus, Nov 10, 2019.

  1. Tantalus

    Tantalus Member

    Jan 15, 2019
    Kerikeri, Bay of Islands, New Zealand
    450 Sundancer 1997
    3116 Cats - 350’s
    14C07727-8AFF-4411-9146-5183F67AFA19.jpeg 20A49DCB-8E8C-4D50-BA2C-D0547C7BB8C3.jpeg 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.
  2. hottoddie

    hottoddie Well-Known Member

    Jan 11, 2012
    Boston/Cape Cod
    1986 Sea Ray 390 EC
    Garmin 4212 Chartplotter
    Garmin 24 HD Radar
    Garmin 546s Plotter
    454 Crusaders
    Sounds like possible bad ground connections behind the dash. Could be causing both the erratic readings on the volt meter and tachs.
  3. atrick

    atrick Active Member

    Mar 4, 2017
    1995 searay 290 Sundancer
    1990 21 maxum
    Twin 4.3 mercrusers with alpha one genII drives
    305 chevy with a alpha one drive
    Check volt reading at back of gauge with vom and see if gauge is reading same
  4. Tantalus

    Tantalus Member

    Jan 15, 2019
    Kerikeri, Bay of Islands, New Zealand
    450 Sundancer 1997
    3116 Cats - 350’s
    Thank you, was going to be my next course of action to test them. Do all the gauges in dash have a common ground?

    Can someone tell me what the small red wire is ( leading to the orange wire) in the image, and even what that is that is bolted on to the front of the alternator? Can these be replaced without having to replace alternator?
  5. Tantalus

    Tantalus Member

    Jan 15, 2019
    Kerikeri, Bay of Islands, New Zealand
    450 Sundancer 1997
    3116 Cats - 350’s
    Is the ground bus bar behind the dash on the 450DA? Or is it in engine bay or behind AC/DC control panel?
  6. Espos4

    Espos4 Well-Known Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    You could run a temporary jumper wire from the ground on the gauge directly to the battery (-) and see if the gauge reading increases.

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