fuel sending unit problem

I've recently bought a 1989 Mitsubishi triton 4 door for my first car and the fuel sender unit stopped working, it had previously worked and read correctly. after buying and installing a new sending unit it only has half the signal so when the sending unit is in the full position the fuel gauge reads half and when the sending unit is at half it reads a quarter at the gauge. i discovered i ordered a sending unit for a k33 model for mine is a k13t, any idea what the difference is and where to buy the correct sending unit or anyway to fix this problem. here's a photo of the model number on the firewall. thanks

http://www.mightyram50.net/vbulletin...id=28367&stc=1