Tachometer Bliss - ByeBye Stewart Warner
Our Defever had the standard, ubiquitous Stewart Warner tachs driven by the alternators. And, of course, they sometimes operated intermittently, a problem that frequently arises on this forum. And even when operative, attaining accuracy by trying to adjust the potentiometer is very difficult if not impossible.
I recently replaced all four of the SW's with "modern" programmable units. The lower helm got VDO's with hour meter and the upper helm got IssPro's. I used the existing wiring taking the signal from the Balmar alternators. Guess what. They work, with no drop-outs. And they are extremely accurate. At 1,650 RPM indicated (by my eye), my optical revolution reader showed 1,644 RPM. My guess as to why the tachs are not dropping out is that the Balmars being controlled by three-stage regulators are always putting out some current even in float stage and that minimal current is all that these new tachs require to operate.
So, for those who are being driven crazy by those old Stewart Warners, you may want to take a chance on a VDO or IssPro. Of course, if your vessel is equipped with a signal generator you are home free. All you will need to know is how many pulses per revolution your pulse generator produces.