Massey 165 fuel gauge sending unit match up

Hi there. I have a Massey 165 diesel that I just bought recently that has a nonfunctioning fuel gauge (or at least is the wrong one for the sending unit.). I have determined that the sending unit works, and has a range of 30 ohms between empty and full, but the gauge won't read it or move at all when hooked up. I can, however, get the needle on the gauge to jump to full by shorting it out with a hot wire, which (I think) tells me that the gauge works but is simply the wrong one for the sending unit.

The next step seems to be to order a new fuel gauge, but every dealer can only match a gauge to the serial number on the tractor, and not to the ohm range on the sending unit. So, the question I have is whether the 30 ohm sending unit is original on the tractor, before I go potentially waste money on the same gauge I already have on it.

After doing some research (including on here - thank you!) I believe that a 30 ohm sending unit is the original part for some 165's, but does anyone know how to find out whether it's the original one for my tractor? My serial # is 9A 49695 which I believe makes it a 1968 model.

Any advice would be much appreciated. Thanks!

don't understand ''shorting out with hotwire'' did you mean GRD wire? fuel guage has I term. for voltage, the other must be grounded to make guage needle swing.

Good point. I'm trying to remember how exactly I got the needle to swing, but I don't think it was as simple as grounding it out (as 0 ohms is empty anyway, so grounding it would just cause it to stay as empty.) Come to think of it, it may have been when I reversed the terminals (just messing around with it to see if I could get it to do *anything*), which would make sense, I think, because the needle would default to the full mark at zero ohms (or at least that's what common sense tells me.)

I'm new to all of this, so I'm fully willing to concede being wrong on any and all of it

I'm not sure what the ohm rating of the sender is, but that it doesn't do anything sounds like there is another problem.

Typically grounding the wire (0 ohm signal) that attaches to the sending unit will cause the gauge to read full. Removing the wire from ground (infinite ohm signal) will cause the gauge to read empty. Some work opposite, but still should cause it to swing full scale.

The dash gauge should be supplied with ignition source voltage to one terminal, the other terminal connects to the sending unit. Some gauges use a regulator to drop the voltage to around 9v, but even if that were bad the gauge should still do something as long as there was voltage to one side and the other grounded.

A common problem with fuel gauges is a missing tank ground. Double check that the sending unit body is grounded, not just to the tank but back to a known good ground.

Thanks for the feedback. My sending unit reads 0 ohms when empty, and 30 when full. If I attach an ohm meter to the wire to the sending unit, and ground it on a good ground on the frame of the tractor, it works (about half a tank, and it reads about 17 ohms.) - so I know the tank ground is ok. A wire from the ignition does go to one terminal on the gauge, and the other goes to the sending unit, but it just doesn't do anything other than show empty.

As I said earlier, what I'm really looking for is to find out whether the 30 ohm sending unit is original for the tractor. The dealers for some reason can't answer that question.

Also make sure the wire from the gauge to the sender has continuity with your ohm meter.Mark

Yep, that it does