Fuel sending unit question(s)

[JNewm]

Hi all! I'm about to replace my fuel sending unit with a new one from MWB and am wondering about wires. The MWB unit has a red wire (coming from a little bit higher up on the plastic box at the bottom of the stem/rod) and a brown wire (coming from lower down on the stem/rod). But my X has the stock red/black wire that goes to the fuel warning indicator and the light-blue/yellow wire that goes to the fuel gauge.

Is there an easy way to tell which wire on the MWB unit should be connected to each stock wire on the car? Or should I just start plugging stuff in and seeing what works?

Also, the unit I got from MWB is different from the stock design--and, frankly, from the photo on MWB's website. The stock design, at least as I recall from when I installed it in the new gas tank a few weeks ago, has a straight rod that connects to a thinner straight rod with the float on the end of it. The one I got has an angled thick rod. Here's a crude drawing of the one I got, next to the photo of the stock-looking unit from the MWB website. Is this okay? Has anyone installed the new/different type of unit? Basically, is this thing gonna work??

 

[JimD]

Pretty sure these are stock units. FI unit on top, carb is the lower unit. I pulled these from the original tanks in my 78 and and an 81 parts car. It looks like the FI unit may have a slight turn near the end of the tube where the sender is mounted. The sender seems to be angled up off the ground in the picture. The bend is probably necessary to position the float where it wont contact the tank walls.

Not sure if it is helpful since it is the carb unit, but here is a picture of the top of the unit before I pulled the tank. My guess is the wiring would be set up the same, but it is a guess. It looks like there is a black ground wire from the harness connected to one of the small sender screws.

 

[JNewm]

Pretty sure these are stock units. FI unit on top, carb is the lower unit.

Thanks for the reply! Hm, okay. Here are a couple of actual photos of the MWB (FI) unit I got. It definitely has a different shape than the stock FI one in your photo.

 

[JimD]

I don't think the shape of the tube is important, as long as it supports the float arm freely inside the tank.

I would install red to red/black. Then hook up the other wire. Did you take a picture of the wires before you disassembled?

 

[JNewm]

I did--red/black is on the left; light blue/yellow is on the right, and it has a ground like your photo above shows.

 

[carl]

MWB is very approachable and will help you with products you buy from them.
As an aside, without a dedicated ground wire the sending unit will not work. This can be missed by those of us who also play with spiders which do not use a ground wire.

 

[JNewm]

Yes! MWB has been great whenever I've had questions... Except that I tried calling this A.M. and they apparently aren't open on Saturdays

At any rate, I just went ahead and replaced the old unit. Apparently I guessed right with the wires! I hooked the light blue/yellow wire up to the terminal located toward the right side of the sending unit and the red/black wire up to the terminal on the left. It works!

Here's the old unit. It has the same bend as the new MWB unit I just installed. @JimD, the closer I look at your photo above, the more I realize your FI unit pictured probably has the same bend--the camera angle is just making it look straighter than it actually is.

 

[JNewm]

Also, I don't know if it shows up in the photo, but the white plastic float on my old unit is about 1/3 full of liquid. That . . . doesn't seem right(?) Wondering if it developed a pinhole leak, such that it became too heavy to actually, well, float.

 

[JimD]

Also, I don't know if it shows up in the photo, but the white plastic float on my old unit is about 1/3 full of liquid. That . . . doesn't seem right(?) Wondering if it developed a pinhole leak, such that it became too heavy to actually, well, float.

That "less than floaty float" is one of the common failures, the other being worn windings on the sender. Here is a picture of the carb unit I pulled out of my 78.

b unit I pulled out of me 78.

 

[Dr.Jeff]

Ya, those plastic floats gradually fill up with fuel...it should be empty. I suspect the plastic allows permeation through the wall. Even a new replacement will likely begin to collect fuel inside eventually. If you find it happens too soon for your liking there are some brass floats that will fit the Fiat sender with minimal work. They were used on older American vehicles and can be found online for around $10.

 

[LarryC]

The float is actually easy to repair. Here is a thread I did on this issue a while back:

Gas Gauge Sender Float Repair

The fuel gauge has steadily moved downward over the years until recent fill ups only showed a 1/4 tank when in fact it was full. Suspecting a fluid-filled sender float, I pulled it and sure enough it was full. I looked it over with a magnifying glass while trying to see if there was a crack or...

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