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Tell me I need a fuel tank sending unit

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M

mightymidget

Jedi Knight
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My $500.00 Midget (68 negative ground) gas gauge is not working. you can ground the one side (wire) of gauge and the needle moves toward F.

Thought I had a bad ground so dropped the tank, The float was stuck. I unstuck. Now it moves freely. This is how I tested the sending unit to determine it is not servicable:

Removed the sending unit from the tank and sat in the front seat of the Midget with it in my lap. Then I hooked the ground wire from the gauge to the sending unit connection. then I grounded the body of the sending unit with a jumper wire to a known ground. gauge did not swing as I grounded or moved the float in the sending unit.

I need a new sending unit ..correct?

Order from one of the main suppliers?
 
If you can open the cover at the top of the sender you will see that it is nothing but some wires wrapped around a core and a (or two) wiper along the sides.
If you clean the wipers (often just running then up and down several times will clean them) it will often work but otherwise you may have a broken wire (how good are you at soldering?)
BillM
 
To test a sending unit, you have to power the gauge with 12 volts hot.
Ground the gauge, run a wire from the "T" (tank) side of the gauge (green/black wire to the sending unit terminal. Also ground the sending unit and then move it.
On a 68 or newer, the current should run through the voltage stabilizer mounted inside the firewall behind the glove box but just to see if it works, the stabilizer is not necessary, it just will not read correct but will go from E to F.
 
To expand a bit on Spritenut's post....

A '68 should have a voltage stabilizer supplying voltage to the fuel gauge. 12V goes "in" on the stabilizer's "B" terminal and 10V (choppy) comes out on the stabilizer's "I" terminal. One side of the fuel gauge should be connected to the stabilizer's "I" terminal with a light green wire. The stabilizer's 10V output is hard to measure accurately with a digital meter.

The green/black wire on the sender should go directly to one of the fuel gauge's spade lugs. On car's with the voltage stabilizer it does not matter which gauge terminal is connected to what. (On the early gauges, the gauge terminals are marked with "T" and "B" so you hook the wires up correctly... that shouldn't be applicable here).

With the ignition on, if you ground the green/black sending wire, the fuel gauge should go to full. If it does, that indicates the gauge is getting power and that the green/black wire is intact.

Some Smiths sending units have an insulated spade lug on them. The green/black wire is connected there. The housing of the sending unit is either grounded through its mounting surface OR by a second spade lug attached (without an insulator) directly to the sending unit housing. To test the sender, you can hook it up electrically as you tried, or you can connect a multimeter across the sender terminals and measure the resistance in Ohms. The later gauges should operate between 270-240 Ohms with the float arm in the down/empty position and close to 30 Ohms when the arm is in the up/full position.

As mentioned above, gum and varnish can deposit on the resistive windings inside the sending unit. If you have a dip bucket of carb cleaner you can soak the sender in that and operate the arm manually for a while to dislodge the deposits. Failing that, you can open the sender up and look for deposits and broken windings. As mentioned above, you can solder breaks... but it is tricky and will require acid flux. With resin flux it will be very hard to tin the resistance wires.
 
Billm said:
If you can open the cover at the top of the sender you will see that it is nothing but some wires wrapped around a core and a (or two) wiper along the sides.
If you clean the wipers (often just running then up and down several times will clean them) it will often work but otherwise you may have a broken wire (how good are you at soldering?)
BillM [/quote

This is the type of sending unit my car has. I have a voltage resister and is in working condition. I am pretty sure everthing works fine until I get to the end if fuel gauge wire at fuel tank.
Click to expand...
 
Billm said:
If you can open the cover at the top of the sender you will see that it is nothing but some wires wrapped around a core and a (or two) wiper along the sides.
If you clean the wipers (often just running then up and down several times will clean them) it will often work but otherwise you may have a broken wire (how good are you at soldering?)
BillM
Click to expand...

BillM
Your Advice is good. I came home today and grabbed my readers and the wifes lighted magnifing glass and after the inspection I found the wire to be open between the coil pack and the spade connector on top of the sending unit.

Repair is simple, if it can be simply done.Thanks for advice

The metal in wire is it solderable with common solder?
can you use another wire to jump from one wire to the other so repair can be done with out trying to butt joint the solder area? if so common copper strand from scrap wiring?


Thanks
 
I have had good luck with common rosin core solder but if Doug says that acid core is better then I will believe him! Just clean it after soldering.
Bill
 
dug up my pos old iron and got the senging unit to work my making a jumper wire out of a wire strand. Will install tomorrow but it bench test fine
 
Brain lock :

Since I had my gas tank out I cleaned and used Eastwoods ecapsulator paint on bottom of the car (not the tank).
I am going to reinstall the gas tank tonight and was thinking about placing an addition ground wire, since grounding seems to be a problem that arises at times.

For the life of me I cann't figure out where to attach the extra ground connector on the sending unit. what is throwing me off is the rubber gasket on the resister cap of the sending unit. is it suppose to be isolated from grounding?
 
Put the extra ground wire on one of the screws holding the sending unit in place. You are trying to make sure the tank and exterior of the sender are grounded good and not just relying on the tank contact to the body and the straps to give you a ground.
 
Well as mention in other post got the car down to a gas station and filled it up with ethel. I guess wires are backwards on the gauge. went from full to empty. Heh but it works !
 
Reminds me of when my buddy told me, "He man, tell me if I hit that tree.".......*CLUNK*...

"Hey man, you just hit that tree."

Hehehehe, he was ~SO~ mad !!!!

"WHY DIDN'T YOU TELL ME I WAS GOING TO HIT IT ?!?!?!?!?!"

"That's not what you asked to do ~man~ !!!!
 
Mightymidget, the gauge should not work backwards if the wires are connected backwards.

A 1968 should have the voltage stabilizer for the gauges. The sending units for those later gauges go from about 270-240 Ohms when empty to about 30 Ohms when full. The early cars had sending units that worked the other direction over a narrower range. Regularman will be able to provide the exact numbers but it should be something like 0-10 Ohms when empty to about 70 Ohms when full.

If you have an early fuel tank/sender with the later fuel gauge, that will read backwards. Likewise, if you have a later sending unit and an early fuel gauge without the voltage stabilizer, that will read backwards. Later gauges are not "connection specific". Early gauges will be marked "B", and "T" on their backs near the connection lugs. B is for the switched 12V power connection and T is for the sending unit wire. If you hook those up wrong the gauge will read wrong. Early gauges need a good ground connection, later gauges only need the ground connection for the lamp to work.
 
This is my problem then, I just grabbed a fuel gauge off ebay. I need to find the proper fuel gauge now. My sending unit is the old style. ANy way to figure out which gauge would be proper. I guess moss catolog will help
 
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