i got a 1989 f-150 4x4 with the 300 inline 6 i just put in a brand new gas tank and fuel pump and now my fuel gauge not working right

 

Can you give a little more information?
What fuel pump is not working, the one on the frame or in one of the tanks?
Do you have two tanks?
If you have two tanks does the other tank work OK?

 

There are two separate devices in the tank. The pump, and the float. If you bent the arm of the float, or cracked the float, it will be stuck in one postion or if the float is cracked and filled with gas , then it will always read empty.
The float assy. sits close to the sidewalls of the midships (front) tank, and it may be jammed up against the inside of the tank wall. come on back bmacky 14

 

i only got the one tank and my fuel gauge goes all over the place half to full to empty to full its not readin proper

 

My best guess would be the plug on top of the tank.
Make sure it is well seated and you used the grease that came with the pump on the plug.

 

it never came with any grease

 

Then you need to go to an auto parts store an buy a small tube of Electrical Dielectic Grease.