Idiot light temp sending unit, which one theres three years

[steveo3318]

I have a temp gauge but I am wanting to add the idiot light as well to my gauges. I know where in lands on the ignition switch and the gauge cluster pinout. but heres my problem. When I look them up on brothers site or anyone elses it says a dummy sending unit for either a 67-68, a 69-70, or a 71-72. Can anyone tell me the differences in these units? Is it thread size or the range in which the temp switch contacts on heat? Thanks guys

I also added a switch for the emergency brake that works in unison with the idiot light on the dash with the brake system. Its nice to see it on instead of burning up brake shoes!