Ignition and fuel gauge wiring

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garethreeves

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Mar 5, 2012
67
hunter 375 Chicago
Hey Guys,

I'm trying to wire in a new fuel gauge and am completely confused about how it should be done. Gauge was broken when I got the boat so I am not sure how it was.

I assume that power should come from the ignition key switch and I would expect power to be applied the the gauge and sending unit only when the key is on. Is that correct?

There are two wires going to the ignition switch and ~12V flowing through them at all times, except when the key is turned and then the voltate goes to zero. This is the opposite of what I was expecting.

Any help is appreciated. Its a 2000 H320.

Thanks

Gareth
 
FourPoints

FourPoints

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Apr 8, 2010
1,606
Frers 33 41426 Westport, CT
Switch should have a circuit that powers 12v+ only when it is turned on.

12v+ (accessory) from switch goes to gauge.
12v- from ground buss or switch goes to gauge
12v- from ground buss goes to sending unit
12v- from ground buss goes to ground strap on fuel tank
pink sensing wire goes from gauge to sending unit.
 
G

garethreeves

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Mar 5, 2012
67
hunter 375 Chicago
Yep. That's what I was expecting.

Keyed ignition switch has three terminals on it. Wires from two of those terminals run to the button you push to start the engine. Voltage across the terminals with wires is 12 until I turn the key on as if starting, then the the voltage drops to zero. If I wire it as suggested it registers on the gauge when the key is off and then drops to zero when the key is turned on.

What am I missing here?

I tried the third terminal on the ignition switch and its zero volts regardless of the key position.


Thanks in advance?
 
FourPoints

FourPoints

.
Apr 8, 2010
1,606
Frers 33 41426 Westport, CT
Hmm, you've got me on that one... are you sure you aren't testing it to ground, and seeing it close to ground in the off position?
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Depends on how you measure it. If you put one terminal on the + battery and the other on the switched side of the ignition switch then when the ignition is off the batter + is at 12 volts and the switched side is at ground (wire goes through the loads to ground) so 12-0=12 on the meter. When you switch the ignition on the switched terminal is now at 12 volts and supplying voltage to the loads so 12-12=0 volts on the meter. this is normal.
BTW, this happens a LOT in DC wiring. As a general rule you should always have on of the voltmeter leads on GROUND and probe with the other. This helps prevent these sorts of head scratching events.
 
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