installing a/m fuel gauge in toyota

I have a 1980 toyota 4x4 pickup that I have converted to offroad only and want to install an aftermarket fuel gauge.  After some research, I have found that I need to know ohm range from full to empty in order to get the correct gauge. I have checked with Toyota and various service centers and no one can tell me what ohm range gauge i need. I have identified the two wires coming out of the float from the top of the fuel tank. I am assuming that one would be positive and one neg, and that the positive would need to be wired to the ign switch, but not sure if there is a relay involved, or etc. Therefore,

What is the proper way to find out the ohm range and properly wire in an a/m gauge so that it works correctly. 

Anyone that has any info or can point me in the right direction would be greatly appreciated!!! 

pics are located here if you are interested in looking... http://www.cardomain.com/ride/722541

hey there,

i am trying to find out the exact same information, if you find out, or any one knows can you please let me know as well.

thanks