Re: gas, speedometer and rpm gauges not working
Pictures aren't really necessary since every gauge except the speedometer needs +12 volts on the "I" terminal when the key is on, ground on the ground terminal, the a signal from the sender (fuel, temperature, trim or whatever) on the "S" terminal. The internal light ("L" terminal) for each gauge is typically fed from the NAV/ANC switch but in some cases that terminal is powered whenever the key is in the RUN position. A voltmeter is needed to verify that voltage is present. If some gauges work and others don't, suspect a sender or sender wiring problem. If none of the gauges work suspect a power or ground problem since all of the gauges are daisy chained from one gauge to the next. Looking at wiring is not a valid check. A multi-tester is your friend here. Speedometers are mechanical devices and require only +12 volts and ground for the internal light. A plastic tube runs from the speedo head to the pitot at the back of the boat. This will be a separate unit or built into the lower unit on the engine. Tachometers have a "sense" signal on the the "S" terminal that originates from the the charging system. If the battery is not being charged (look at the voltmeter) then that would account for the tachometer not working either. Fuel senders are typically 33 - 240 ohm resistive devices. You need a multitester to verify operation of any sender. If you use the search feature in this forum you will find a multitude of Fuel Gauge troubleshooting posts, most with diagrams and testing procedures. Other gauges work on the same principle. None of them work without +12 volts, ground and the sense signal.
