What is the value of a 1971 f100 in fair condition?

rule of thumb is easy equation

for a 1971 model you simply multiply the first 2 digits of the year with the last 2 digits then divide by 2.....

i.e -

19 x 71 = 1349 / 2 = 674.50

so to conclude this theory your truck is currently valued @ $674 and fifty small

hope this helps :)