fuel gauge replacement

Alright, I've got to be honest so here it goes. Fuel gauge took a dump after just installing two new batteries. It was shady at the end of last season so I had a feeling it was going to let me down sooner than later. Looked for about a week online for the exact replacement Faria gauge. No luck, so last Sunday, I went to Pep Boys and bought a fuel gauge and made an attempt to install. (I know it's a no no!) Incoming! lmao! Anyway, you guessed it! Doesn't work because of different ohms range of resistance. Hooked everything up correctly and gauge read (E). Double checked everything with a led test light at the sender pole at back of gauge and the main ground holding it on the entire time. Guess what? It read accurately. The second I removed it, gauge went back to (E). Did the same on the tank side and the gauge read accurately as well but only if I held the led light to both poles on tank. I guess whatever resistance that was created by the draw of the led light was just enough to offset to make compatible with sender in tank. I also checked the sender unit in tank thinking that could very well be the culprit because I wasn't absolutely sure the old gauge was bad until I removed it and put 12 volt to it. The old gauge did nothing instead of pegging to (F) as it should. So, I was back to square one. Went back online and after about an hour and a half, found the exact gauge brand new somewhere on ebay. Ordered it and just got it today. Still have to install when I get a chance this week. Anyway, I kind of knew from the start that the auto gauge was a fail but guess I had to see and learn for myself. At this point , I am thinking that the sender in tank is working as it should.
(I hope) Again, I removed tank sender and float and all looked well. The Faria marine gauge uses an ohms range of something like 240-30 ohms resistance. Not sure how the ohms works on the auto gauge that I spent $20.00 on like a dummy! lol Oh well, chalk it up for experience I guess. I just hope the gauge is the problem and not the sender. From the information I have given you men I was hoping that you guys might be able to diagnose or lead me in the right direction on this. One last thing all wiring and connectors are as clean as a whistle and as previously mentioned everything was working until spring startup. Also, I am getting 12 volt to gauge from (I) switch and there is an excellent ground. Thanks, Tom

Ayuh,... The gauge measures the varying resistance to ground, through the sender....

At the tank sender, touchin' the gauge wire to ground will peg the gauge to Full...

It sounds like the tank/ sender ain't seein' a Good ground...

The filler neck should be bonded to the tank, 'n the tank should be bonded to the motor's block, which is grounded to the battery, completin' the circuit...

The fuel guage is 80 - 240 ohm

The sending unit can be checked with an ohm meter. one lead to any metal surface (of the sender) and the other to the sender terminal.

As you move the float up or down the meter reading should change accordingly. Digital meter will be somewhat tougher to see a smooth change than a anolouge meter Resistance should be set to 1K on meter. Test light is not used for this test (NO VOLTAGE)

As Bondo said the ground NEEDS to be 100% or the guage will malfunction.

The sending unit does NOT have any voltage to it........ZERO, it is nothing but a variable resistor. Power only goes to the guage to power it and it alone.

One issue I have come across is the top plate of the sending unit which should have a ground spade sticking out of it and the underside plate (typically connected by rivits or screws or simply bent tangs) can and does loose its continuity. If you pull the sendor out of the tank make sure you check with a ohm meter the top and under plate and make sure there is NO resistance. (meter will react as if you touched both probes to the same metal surface)

I have a suspicious feeling the store purchased guage is ok.....

Thanks Bondo and kghost for the quick response. I will do as you suggested. I will report back later this week with my conclusion. Thanks, Tom

Perhaps this may help in your troubleshooting

2X on the ground at the sender...

Most domestic gauge makers use the american standard where a 240 ohm resistance at the sender terminal (to ground) will show the "low" value of the gauge and a 33 ohm resistance will show full scale deflection...if it is handy, a 110 ohm resistor will make the gauge go to 1/2 way.

Installed new gauge and still nothing! I will do as you guys suggested. Either the sender took a dump or I have a ground issue. I have a Mueller 40 gallon belly tank if that helps. The tank sender looks pretty cheesy if you ask me but that is just my observation. lol Also, I did wire the gauge correctly with ignition switch to the off position. The gauge is identical and like I said before, the gauge worked until late last season then it seemed to bounce a lot if that means anything. If I do replace the tank sender, if possible, might think of something a little more durable. I guess the poor thing gets the puss knocked out of it so I guess I am due for a sender as well. I will try everything above and let you guys know how it goes later this week. Ran out of time because of work. Getting into busy season but will probably put an eyeball on it on Saturday. Thanks again to all of you guys for the awesome support as always! All the best, Tom

Finally got around to replacing my sending unit. It was indeed the tank sender unit. One question for you guys: What are the odds of both fuel gauge and tank sender unit failing simultaneously? Tested both and both failed miserably!
Everything now is working as it should! I was able to find the correct oem Mueller replacement sender so it made it easy to repair but gave me the heebeejeebees around all of that gasoline. Thank God I don't have carpet in my boat! Can you imagine rubbing your shoes like you did when you were a kid and trying to install an in tank sender? ZZZAAAPPP! Caboooom! lmao! Boat is almost ready for striper fishing. Exaust shutters need replacing and after that she should be good to go! Never been ready this early. ahope it's not a bad omen! lol Last two seasons it seems like all I did was work on boat. Season passes by so quickly. Economy is definitely picking up now so hopefully I will be able to get out a bit more this season. Thanks again fellas for all the great support as usual! sincerely, Tom

odds of both failing at the same time....? Unless lightning strike got them or there was some abuse to the electrical system, I'd say very low...

That was my exact thoughts too makomark. I guess I must have goofed somewhere. Don't remember it happening but I guess anything is possible. thanks, Tom