gas gauge always reading full how to fix it right?

Question

wired to a toggle switch ,with switch on barely moves any suggestion?

on a1977 boat

Answer 1

Old. So, check the Sending unit in the Fuel tank. They go bad in time. You can remove it and use an Analog Multimeter to OHM it, one lead to ground and one to the send Screw. When you move the float it should move the meter in a smooth manner and not jumping around. Then check the Condition of your wires and Connections, may actually check this first. Last check the Gage it susceptible to water damage over the years.
I will almost go with the Sending unit as I have replaced them most. They become Corroded over time from Moisture in the Fuel I guess.
Wal-Wort and Auto Parts stores may have the Multimeter for $10-15. well worth the money over time for many other uses. Just learn how it work so you not mess it up.

Answer 2

Possibles Only: polarity to gauge wrong(+ and - reversed) check for markings on gauge.
Corroded connections or high resistance, broken wiring if the fuel gauge is a resistance type either in the sender or the dial.
Mechanical problem with the sending unit at the tank.
In a boat there is lots of moisture so ther is lots of chance for rust and for electrolytic corrosion between different metals, like copper or aluminium and steel. wiring rots from chemical reactions with other metals and water, especially with electricity in the wiring. sacrificial anodes are blocks of zinc that are meant to react more strongly than the other metals and rot away first, to protect the more expensive and important metal parts of your boat.
Not much help,I know, sorry, if you get a cheap multimeter/ohm meter it will let you check for resistances in the wiring, the gauges, and for the polarity of the connections. Good luck, always check the easiest and cheapest part to fix first, in this case it might be a problem with the gauge itself,and simply be the easiest way to fix is to replace.
forgot to mention wiring might be pinch and short circuiting thruogh the insulation on the wiring some where between the sender and the guage dial

Answer 3

You need to find out if it is the dash gauge or tahr tnk sender. If oy can ground the wire at he tank and have someone watch the gauge with the ign. switch on wire unpluged and grounded = full (Takes a few seconds.)