The gauge hasn’t got a clue...

Canal Boat - - Back Cabin: - MICKEAMES, via the CB TONY REPLIES…

The tem­per­a­ture gauge on the deluxe power panel con­nected to my Lis­ter LPWS4 has started flap­ping about all over the place. I have tried short­ing the sender, but the gauge did not go to high. Any idea of the cause?

Qweb­site

Th­ese are nor­mally bi-coil gauges and if the coil that is earthed (neg­a­tive) gets an open cir­cuit then the gauge will flick to full scale de­flec­tion. But while an in­ter­mit­tent earth fault may ex­plain the flap­ping about, it does not ex­plain why earth­ing the wire at the sender does not give full-scale

Ade­flec­tion at least some of the time. This sug­gests the prob­lem may be in the pos­i­tive side or, more likely, on the ca­ble be­tween gauge and sender. A multi-plug con­nec­tor on the main en­gine wiring har­ness may have de­vel­oped a loose or dirty con­nec­tion.

If the wiring has no faults, you are left with a faulty gauge – save for one thing: many more mod­ern Lis­ters use a re­lay that pro­vides a neg­a­tive path when start­ing, rather than sim­ply hav­ing an earth re­turn. If this plays up (es­pe­cially in­ter­mit­tently, as with a loose or dirty con­nec­tion) it might give odd symp­toms. How­ever, I would ex­pect this to cause start­ing prob­lems be­fore gauge prob­lems.

So ba­si­cally, check all the wiring and con­nec­tions, and if all is well, change the gauge.

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