Hi I put a new fuel gauge in my 81 f250 and it is reading backwards it says full on empty and empty on full and help would be nice

 

Did you put a new gauge in the dash? or a new sending unit in the tank?

 

I took a gauge from an 87 f250 I have been parting out and that won't read right so I got a new gauge and now it reeds backwards

 

Pretty sure 1987 was the year they changed resistance values from 72 ohms empty and 12 ohms full to whatever it got changed to. So, that's why that one wouldn't read right. What happened to the original gauge? usually they read backwards when the resistance values in the sender are backwards.

 

I have the originals in my truck the one out of the 87 dosent work so I was trying to use the one out of my 81 the sending units are different so I might switch out the tanks and get a new sending unit for the 87 tank

 

I would recommend you remove the sending unit from the tank and check the resistance values with an ohm meter. It should read 72 empty and 12 full (+/- 5 Ohm's are acceptable from sock readings) does it have it's original sender in the tank?

 

Yes I have the originals for my set of tanks out of my 81 and one for my set of tanks out of my 87

 

I swapped out the dash from the 87 in to my 81 that is why I don't have the gauge out of the 81 any more

 

Well that's why. Get a new 87 sending unit then and make the 87 fuel gauge work (if it's not) it should work right. the 87 and newer resistance values are 16 ohms empty and 158 full. They are backwards of the older style and that is why it is reading backwards with the 87 cluster.

 

Ok I will try that thanks

 

One thing I forgot to mention, the 87 sending unit has a wider mouth than the 81. You will need to install the 85 and up style gas tank with the wider sending unit mouth.

 

I just did an ohm reading on the 87 sending unit it is 36 empty and 186 full I know about the tank size and when i hook it up to the gauge from the 87 truck it stays on 1/4 tank no mater what and on the new gauge I hot it sits at 1/2

 

Should work alright.

 

It dosent the gauge on the cluster reads 1/4 when it's hooked up and the new gauge I got reads 1/2

 

Aren't these things just a joy to work with? sounds like it's time for a new one!