T&T: Phantom Voltage Loss - was Cummins 5.9 High Output Alternator...

[Dave Legrow]

>A brand new installed Rule Bilge pump that won't pump. There appears to 
>be nothing wrong with it. But, the voltage goes to zero when the on 
>switch is activated, but if it's a short the breaker is not tripping...
>And it's wired with the correct polarity; just to stay a step ahead of 
>you super sleuths, the pump was replaced and still the same result.

>I'd bet 99:1 that this was caused by a corroded fuse holder or a failed
>breaker, resulting in a high-resistance connection. The quickest way to
>detect this is to place a voltmeter across the fuse or breaker with the >load
>off. Voltage should be zero. The apply the load and see what the voltage >is.
>If it's anything other than zero you have found your culprit.

Corrosion sounds like the culprit to me as  well.  but since this appears widespread, I would suspect corrosion more likely, but not neccessarily, on the ground connection.  If there is a wiring harness, check the mating plugs on the harness. I chased problems like that for a year before I decided to remove and dremel polish every brass ring connector on the boat ( almost all the crimps were good - the rings themselves didn't make good connections due to surface corrosion), and replaced one of the wiring harness connectors. Nary a problem after that!

Dave Legrow
on the Delaware River