Fuel Gauge reads backward

sailak · #1 (**permalink**) 02-17-2010

I bought a new fuel sending unit since mine no longer functioned. Today while installing and testing I found that it reads backward -- when the float is "up" the gauge reads empty, when the float is "down" the gauge reads full.

I switched the wires on the sending unit, same results. I do not see anyway to swap the float arm around.

Any ideas?

The gauge is a VDO brand that I assume came with the boat in 1986. The new sending unit is a Moeller...part number 35772-10.

Thanks for your help.

I33 · #2 (**permalink**) 02-17-2010

I've seen this before. The sender and the gauge need to be matched. It sounds like your old VDO is not matched to the new sender. Swap one or the other, but get a matching set and you should be fine.

SecondWindNC · #3 (**permalink**) 02-17-2010

Magic marker?

F --> --> --> E

(just kidding)

bljones · #4 (**permalink**) 02-17-2010

You're sure you haven't wired it backward?

sailak · #5 (**permalink**) 02-17-2010

Secondwind...don't think I didn't think about doing that.

The gauge I didn't touch. The sending unit I tried reversing the wires but no effect on the gauge reading.

timangiel · #6 (**permalink**) 02-18-2010

reversing the wires isn't going to do anything because it is basically a variable resistor and its resistance has nothing to do with polarity. as the arm is raised the resistance should decrease, allowing more current to flow causing the needle on the gauge to deflect farther and vise versa when it is lowered. its behaving as if it is installed upside down, but I can't imagine how that could be possible.

Pub911 · #7 (**permalink**) 02-18-2010

Maybe you've capsized. Sorry, couldn't resist.

US27inKS · #8 (**permalink**) 02-18-2010

Some senders are made to swap the arm to the other side, some are not. If you can't swap the arm, and you can't get a correct sender, cut the arm off and weld it on the other way. You may have to be a little inventive to get it done, but I'm sure it can be done. Just don't burn the sender.

wind_magic · #9 (**permalink**) 02-18-2010

Did you buy a sender made for the southern hemisphere ?

It sounds like you installed the fuel tank upside down.

Seriously, I'd PM btrayfors, he probably has some simple op amp circuit that will reverse the voltage for you that won't require modification of the sender.

Stillraining · #10 (**permalink**) 02-18-2010

Dang I hate my memory...I had this issue as well and I cant remember how I fixed it.. but I did..and I dont think it was taking it back but it might have been....Sorry