The Stovebolt Site Forums The Shop Area The Electrical Bay Checking new Sending Unit/guage UPDATE

....OK you electronics guys lets keep it simple.
I have a new sending unit and a new Runtz reducer to hook behind the guage. The guage (it checked good) is out of the truck.
I would like to bench check sending unit for accuracy, and the guage, BEFORE I put it in the tank and install on the panel.... .mainly to see if halfway on the sending unit is really 1/2 a tank on the guage.

Now, can one of you guru's walk me STEP BY STEP on how to hook this up on my work bench, hopefully using a battery charger, or I could get a battery.

...and as a side note I guess I need to know which terminal is the Battery terminal on back of the guage before I even start.
Be patience with me Grasshopper. Electricity is not my thing.

Hy Achipmunk, if you have and can use a 6 volt battery, you won't have to add the runtz into the circuit for testing purposes. If you have an ohmeter you can check the sending unit first before testing the whole system. Connect one lead of the ohmeter to the output stud of the sending unit, connect the other lead to a good clean part of the housing, with these connections in place, slowly lift the float arm up and watch the reading on the meter, it should go from 90 ohms to zero, or the other way around I can't remember which way it reads. If it passes that test then you can wire it to the gauge, output of sender to gauge terminal of gauge, gauge may be marked on the back "ign", or "+" that is the power terminal, the other terminal may be marked "ga" or "sen", that is the terminal that you want to hook the wire from the sending unit to. You must also connect a ground wire from a clean spot on the sending unit housing to part of the gauge frame, not to a terminal but to the metal frame around the operating coils, and of course back to the battery ground. So power to the power teminal of the gauge, sending unit output stud to the other terminal of the gauge, and a ground wire connecting the battery, the sending unit housing, and the gauge frame. Now slowly lift the sending unit arm and observe the gauge operation, I hope y'all can understand that, it does sound complcated, but I don't think I've left anything out, good luck, and remember if the smoke leaks out of the wires you've done something wrong

... thanks Bobb. After Breakfast tomorrow I think I'll spend some time at the work bench. I blasted and painted the housing and don't remember seeing any markings but I may have forgotten. I'll look good before I start. Someone told me there are two aize's of terminals on the gas guage and that the small one is the one for the battery. I seem to remember that when I did the guages about a year ago. I"ll dig everything out tomorrow.
Thanks again.

Hi Achipmunk, Pulled diagram from my new harness install and it has 12v to E (empty) terminal and F (Full) terminal to sending unit. Hope this helps, good luck with it.

....thanks ya'll. I will get to the shop tomorrow...lor Tuesday. I've been quite busy the past few days with other things....and the driveline guy told me Friday I can come pick up my driveshaft. A short run up the street may be in line soon.....

UPDATE: boy, now I'm really confused and also :mad:
First-- I have a new sending unit for my 52panel tank. I also have a Runtz reducer attached to the Plus(+) side of the guage which by the way is the smaller of the two post on the back of the guage and the guage checked good when I had D&M Restorations check it out.

Well, I hooked it up like 3B said and the hand was just below the "E" mark and when I raised the float it went up to between empty and a 1/4 tank. NOT GOOD...not even close.

Well, another friend of mine tried to simplify it for me, you know A..B..C..D.. and I hooked it up again the way he suggested which was really the same way as Bobb but when I plugged in the battery charger this time the needle went up between the empty and 1/4 tank.. BUT this time when I raised the float the needle went Backwards!!
Well, I tried and tried again but now the cotton picking thing will do nothing! Checked connections, made sure it was grounded good and still nothing.

For quite a while I'ver read about the fuel guage/sender unit problems and was sure I'd lick the problem when my time come to install mine. Yet, here I am with the same thing I've read about for years.
There has to be a good explanation out there somewhere?

Any Suggestions?? At this point I'm ready to cut a hole in the floor and tank and use a measuring stick! Help me before I end up doing something stupid and paying dearly for it later. What am I doing wrong?

Hy Achipmunk, did you check the sending unit first with the ohmeter? If you hook the power up to the gauge and the ground to the gauge frame, and then very momentarily ground the gauge sending unit terminal to ground, the gauge should move through its full range of motion, if it doesn't the gauge is faulty. I can't stress enough that this connection should be very quick and very short duration. Make those checks and get back to us, good luck.

Hi Alvin (or do we all call you eh Chipmunk now),

Don't know if I can add much to the fuel gauge discussion, but I've been wanting to tell you thanks for the great write up on your visit to the Pacific Northwest. But to stay on topic...

There are two electromagnets in the fuel gauge. One pulls the needle toward empty and the other toward full. When the tank is empty and the sending unit drops down, current flows in the circuit that powers the electromagnet that pulls the needle toward empty.

As the float is raised up and resistance increases in the sending unit less current flows to the electromagnet pulling the needle down and more current flows to the electromagnet that pulls the needle toward full. It's kind of a balancing act.

So if you hook up power to the fuel gauge and very briefly ground the gauge cluster (without the sending unit connected) the electromagnet pulling the needle up will (should) read full. If you power the gauge and very briefly ground the sending unit terminal the electromagnet pulling the needle down will be fully operational and the needle will register just a tad bit up from empty.

Best of luck.

Well, after all this "monkeying around", as I call it, I found out today the sending unit has to be bad. I checked it with the ohm meter today and there is virutally no resistance. With the float all the way down (as if empty) the ohm meter reads "0".
No matter how slow/fast I raise the float the hand will not move. No resistance what so ever. (yes, I had new batteries in the ohm meter)

As I look back and rethink everything, its seems at first I could "feel" the arm rubbing the little spring inside but it didn't feel the same way going up and down, and I could only "feel" it in about half the travel. I say its some bad Tiawanese stuff and will call the vendor tomorrow. I really want to take it apart but I know it will "void my warrantee".

Just as a reminder I had the guage checked by D&M Restorations and it worked fine.... also remember I'm working with the sending unit and guage on my work bench and that its for a "square" suburban/panel tank.

Thanks guys and I'm always open to comments....to learn.

Eileen, its perfectly OOOK to call me Eh Chipmunk and I have the cooking apron to prove it.

the aftermarket sending units are somewhat "marginal" in quality at best but well "better than nothing". i installed both sending unit and gauge (both aftermarket) repops and the sending unit failed shortly after installation for the new owner.

All books say the number one cause of gas gauge problems is GROUND!!!

...you can take my word on the fact that I know it was grounded. I use the alligator clips and make sure it has a "clean" place to bite into.... plus the usual "rub hard" "press hard" ect ect ect.....the think just plain out won't work!.... but Bartamos, your statement is correct!

Hy Achipmunk, Classic instruments makes a sending unit, their p/n SN36, "0" ohms empty, "30" ohms full, which is what is required for your gauge. These are a high quality made in North America product, I have installed two of them so far, and no problems, they can even supply an adjustable length unit, or custom taylor one, go to their website and have a look, price is more than most catalogue stuff, but then "you get what you pay for" don't you, hope that helps.

Thanks Bobb, actually I just got off the phone with my vendor and he is sending me another new one today. He was very nice about and since mine was perhaps the first one out of a new shipment he will probably be checking each one of them....at least the one he's sending me!!
So, we'll see how it does and if not satisfied I'll try your contact. I'll take a look anyway as information.

In the meantime I just finished put my new shiny aluminum driveshaft in the panel....one piece at a time. Gosh, I can almost hear this thing running !!!

Did You take a PIC.of the shaft?????????????????

Pete

yeah I did Pete

http://i140.photobucket.com/albums/r19/LutherParris/52Panel/DriveshaftPanelpics001.jpg

http://i140.photobucket.com/albums/r19/LutherParris/52Panel/DriveshaftPanelpics002.jpg

So I don't hijack my own thread I should mention that I also took a pic of the old sending unit and the new one....side by side. The new one is about 2" shorter than the old one. The old one would actually just about touch the bottom of the tank while the new unit will be at "empty" and be a good inch or so off the bottom. I suppose as long as it registers full and empty its good to go. At least with the new one when it says empty I'll know I have a gallon or two left....but don't we all have to run out of gas once to see where "empty" really is? !!

Alvin put a hole in the side and I'll send you one of the extra dip sticks i have so you can check the level.

So in this post you mentioned that you had a Runtz reducer. Is it a two terminal device or a three terminal device? If it is a three terminal device, you need all three in the circuit for it to work.

It has two holes. One to put on the small (battery) post and the other end to hook the normal wires....oh, and it has a Black ground wire to go behind the nut that holds the guage in the dash.

Here is a pic... don't laugh at my temporary pigtails...I may even decide to do a "quick disconnect" in case I have to pull the guages. I'm to old to stay bent under there to long!!

http://i140.photobucket.com/albums/r19/LutherParris/52Panel/DriveshaftPanelpics003.jpg

That's correct, if ya don't know it will be puzzling from now on.

OK, when you are testing with the Runtz, you must have that ground hooked up in order for it to work. That Runtz looks like a pretty nice little unit, very convenient.

...thanks truckernix. Believe me I did have the little black wire of the Runtz grounded good. My new sending unit should be here tomorrow. If all goes well maybe this weekend I'll have the tank in and gas in it.....which means I'm just about ready to fire this bad boy off!

Hy Achipmunk, do we have an update on this topic yet???

Hi Bobb. I got my new replacement sending unit from the parts vendor BUT according to MY checking I still don't have a good one. Now I'm suspious that maybe my ohm meter is bad?????

Here's what I have done.
While waiting on the replacement sending unit I took all my guages over to my friend at D&M Restorations. Mike has done guages for me, and a lot of other folks, for over 15 years that I know of and many years when he was up in Mass. He is top notch. He checked all my guages, and repaired one, along with the speedometer about a year ago.

NOW....I have the new sending unit and TOMORROW I will go over to D&M and see whats up. Its only about 25 miles and there is a good hot dog place close by!! I am taking BOTH of the sending units with me for HIM to test... AND to check the sending unit with the guage. I'm gonna do this ONE Time and do it right. I ain't gonna pull this tank back off.
I suppose there is a possibility my meter has malfunctioned someway but I'll have to see it to believe it.

I'll get the run down tomorrow and I'll let you know. If I am wrong I'll admit it, send one sender back and money for the postage they spent! We'll see.

Hy Achipmunk, we can't ask for anything more than that, good luck.

Well guys, here is THE scoop.

Went over to D&M Restorations today and had Mike to check the sending units. BOTH checked good. They also registered correctly with my guage. Yipppeeeee.

I just got off the phone with the Vendor and APOLOGIZED. I'm sending one of the units back. I offered to drop in the shipping charges for the "second" unit and was told to not worry about it.

While at D&M I decided to have Mike set up my fuel guage for 12 volts so I will not use a reducer.

THE PROBLEM: My SWITCH on my ohm meter just plain don't work. ..at least correctly. I stopped on the way home and bought me a new digital tester and yes, with it the sending unit checks good!
The "old" meter is in the TRASH CAN...I did save the new batteries.

CASE CLOSED

Hy Achipmunk, thanks for that report, isn't it a pain when our tools let us down. Just a tip, when I'm doing resistance/continuity tests, I always touch the two probes together and make sure the meter reads zero ohms, before continuing my tests, this tests/verifies the meter, and makes sure there is something left in the battery. The old analogue meters had an ohms zeroing wheel which you had to use to set the meter to zero ohms when you touched the two probes together, and I guess that is why I still verify the meter function before using it.

close the book on this one, now on to the next item on the list, keep us posted,

Fuel gauge and sending unit problems sure seem to be tough to solve. I've checked everything out on my Panel (gauge, sender, wiring, grounds, etc.) yet for whatever reason, my gauge always reads " 1/4 " whether the tank is empty or full. When I turn the ignition off, it reads Empty. I like Achipmunk's solution by putting a hole in the floor and tank and using a measuring stick!