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Fuel tank sending unit replacement
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uncle-buck View Drop Down
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    Posted: November-27-2024 at 10:23pm
I think I saw that post a few months ago in some search results.

Ended up with a KUS reed type sender which will be fine for my purposes.
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
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KENO View Drop Down
Grand Poobah
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Points: 11127 		Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: November-27-2024 at 5:59pm
Here's something else that's good to know in the quote below from an old thread

Originally posted by KENO KENO wrote:

Well Dave, just tell yourself you got a better sender than the swinging arm sender with a heavy gas saturated float Wink

One thing most people don't realize with these reed switch type gauges is that inside the tube there are a number of reed switches and the black float around the tube is a magnet that as it moves, picks up a reed switch as it goes past it.

There are only a certain number of switches depending on the length, but on the typical 10 inch or so sender you'll have one switch for empty, one for full, and for example 7 in between them so your gauge only changes readings about every 1/8 of a tank.(If it was a rectangular symettrically shaped tank)

So as you fill the tank, it may take some gas to start making the float actually start moving, then the level gauge responds in 1/8 tank increments. Same thing on the way down.

You'll never know that you have 7/16 of a tank for example, because the gauge will jump from 3/8 to 1/2

Or if you're getting low and it's on 1/8, the next reading will be empty It won't creep down slowly.

Somebody might say "that's not very accurate" compared to the swing arm type that changes resistance and the gauge reading every time it moves, but it also doesn't bounce around nearly as much as the swing arm type. So the reed switch is less sensitive, less precise or less accurate to small level changes but it's not really a problem, especially if you know how they work.
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uncle-buck View Drop Down
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Originally posted by KENO KENO wrote:

The green wire doesn't come from the gauge or have anything to do with reading fuel level

You'll find the other end of the green wire hooked to the gas fill connection. It's hooked to one of the machine screws holding your fill connection to the deck of the boat and it just shares a ground connection with the sending unit.

It grounds the fill connection to dissipate any static electricity while you're filling the tank to minimize the chances of an explosion



Good to know - and thanks again for your help.
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
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KENO View Drop Down
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The green wire doesn't come from the gauge or have anything to do with reading fuel level

You'll find the other end of the green wire hooked to the gas fill connection. It's hooked to one of the machine screws holding your fill connection to the deck of the boat and it just shares a ground connection with the sending unit.

It grounds the fill connection to dissipate any static electricity while you're filling the tank to minimize the chances of an explosion
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uncle-buck View Drop Down
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Points: 331 		Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: November-26-2024 at 8:29pm
Much appreciated, Ken.

I connected the pink wires to each other and the green and black wires from the gauge to the black wire on the sending unit.

Back in business...
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
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KENO View Drop Down
Grand Poobah
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Here's a non artist's rendition of the back of a fuel gauge Wink

You'll have

 A terminal marked "I". It gets 12 volt power when the keyswitch is in the Start or Run position (purple wire)

A terminal marked "S".It runs between the sending unit and the gauge (pink wire)

A terminal marked "G". )Black wire) It goes to ground and to the black wire at the sending unit 

You need those 3 wires for the gauge to function, the blue wire is just for the gauge light.

The terminals are marked on the gauge housing and can be in different positions than the drawing, so look for the markings


So you hook the black and pink wires to the new sending unit wires and with the gauge wired like this, it should work.
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uncle-buck View Drop Down
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KENO, I purchased a KUS reed type sending unit which is scheduled to be delivered tomorrow.

Read the thread you linked, but am still not clear on what to do with the third wire from the fuel gauge or dashboard.

Thanks, as always, for your help.
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
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KENO View Drop Down
Grand Poobah
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Points: 11127 		Post Options Post Options   Thanks (1) Thanks(1)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: November-21-2024 at 7:02am
It might help to know what you bought for a sending unit Wink

Here's your thread from last year in the link.

link

Guessing that you bought one of the reed switch types, here's a link to a thread with some wiring info
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uncle-buck View Drop Down
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I want to replace the fuel tank sending unit in my 90 SN. The fuel gauge itself has been tested and appears to be good

The replacement sending unit has only two wires, but the gauge has three wires.

How can I find out how to connect the new sending unit to the old three wire fuel gauge?
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
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