Fuel gauge problem?!?

[NW Redneck]

Should have known after a great trip with no problems something would have to go wrong......

Everything working perfectly yesterday. Today went & tidied up the boat for the next outing. Turned on battery switch & key to first position (switched power on) and my fuel gauge didn't move. (I know there's between 1/3 to 1/2 tank) All other gauges/lights sprang to life like normal. Checked all connections on back of gauge and at sending unit on tank and all are tight & clean. I had cleaned and applied electrical grease on everything last year. I disconnected all the wires from the back of the gauge except the lead to the sending unit and attached jumpers from ignition 12v to 'S' (switched power-purple wire) on fuel gauge and from gauge to good ground. I'm reading 12.16v from ground to 'S' and 7.92v from ground to 'L' (sending unit terminal). I also get 7.92v from ground to the sending unit lead connection at the tank. I'm thinking the gauge is shot and was wondering if there is any other way to test it or have I prety much covered it?

Thanks in advance!

 

[jevery]

Re: Fuel gauge problem?!?

To test an analog fuel gauge:

TEST ONE

* Turn the ignition switch to the ?OFF? position
* Remove the input wire from the sending unit from the back of the gauge (the terminal is usually marked ?S?)
* Turn the ignition switch to the ?RUN? position (key all the way to the right, without starting the engine)
* The needle on the gauge should be in the ?EMPTY? position

TEST TWO

* Turn the ignition switch to the ?OFF? position
* Attach a jumper wire from the sending unit input terminal (?S?), to the ground terminal (might be marked ?G?)
* Turn the ignition switch to the ?RUN? position (key all the way to the right, without starting the engine)
* The needle on the gauge should be in the ?Full? position

If the gauge doesn?t pass either of these tests, replace the gauge.


From this article,
http://www.trailerboats.com/output.cfm?id=1476505&sectionid=317

 

[hard-3]

Re: Fuel gauge problem?!?

Check the ground wire from the fuel tank sender. the gauge gets its ground to work from the sender. take the wire off the sender and ground it as suggested in previous post . gauge should read full scale when ignition turned to run. if gauge reads full then replace sender. read with ohm meter from terminal on sender to sender body should have resistance not open. if you take wire off sender and go from wire to ground with voltmeter should read battery voltage.

 

[NW Redneck]

Re: Fuel gauge problem?!?

Thanks for the info and link jevery. Now you got me wondering. Has my gauge been wired wrong from the start? The way it is now is the way it was when I got the boat. When I went through cleaning/checking all the connections on the backs of all my gauges I only took the wire(s) off of one terminal at a time, cleaned/greased, then re-attached before removing the next one so I don't think I switched any around. And it has been working fine for the past couple of years the way it is.
OK, I just snapped a pic:

The blue wire on the left is for the gauge light
The upper right terminal marked 'S' was a purple wire from my ignition switch switched power terminal (disconnected here while I was testing)
The lower right terminal looks like it's marked 'L' and is run to the sending unit terminal
The two terminals on the middle 'bar' marked 'GND' are to ground.

If this was backwards, how has it been working until now?!? Should I try disconnecting the sending unit wire and hook 12v to the 'L' terminal, leave the 'S' unhooked and try the above test?

 

[jevery]

Re: Fuel gauge problem?!?

Now that's interesting. Purple is surely 12V ignition and it's connected to S. And sending lead is attached to L. Wonder what L stands for? Or is it an I for ignition? Sure appears to be wired backward, but at this point I'm not going to be the one to tell you to start switching wires around. If it was mine, though, I'd switch em.

 

[NW Redneck]

Re: Fuel gauge problem?!?

Allright, here's what I found. I tried the tests and on test one, with power supplied to 'L' (or possibly I) and sender lead off, the gauge didn't move. With a jumper wire between 'S' and ground, it pegged out way below Empty.

With the jumper on 'L or I', It pegged out over full. Jumper back off, and it read just below E, but not pegged out as with S-G jumped. Weather by design or fault, my gauge seems to work backwards. I wonder if it is hooked up backwards the first time, it will work backwards from there on?

I checked the resistance on the sender (which does have a ground wire from the sender mounting plate to the main engine ground) and it read 123 ohms, which according to the specs in the link jevery posted (25-50 full to 225-250 empty) should be about right for the ammount of fuel in the tank (1/3-1/2 full).

It seems like the gauge itself got stuck somehow. I seem to remember one time just after getting the boat running when I first got it, seeing some slight condensation form on the inside of the gauge glass. It didn't happen again so I didn't think anything of it at the time. Now I'm thinking there may be some internal corrosion/moisture damage so I think it's time for a new gauge.

Thanks for the replies guys. Once again iBoats proves to be a great resource! Sometimes just posting the problem helps to think it through and work out the solution. I love this place.