96...
There are two routes I have seen:
1) buy a controller ($30 on summit) with a temp probe....depending on where you place the probe will determine how often the fans kick on. (there are writeups on here with photos describing the install)
2) wire the fan with a harness directly to your yukon's computer...this is a bit more expensive b/c you will need your computer programmed plus the harness.
Just yesterday I went the #2 route and purchased the items from BlackBear performance. I'm a stickler for the factory look which is why I purchased his harness and I'm having him program my computer to turn on the fan.
From what I saw, there is a 17" and 18" Lincoln Fan. I went with the 18" fan b/c i was told it fits perfectly within our shroud with little modification and pushes the most air...that info was from a poster on this forum. Also, there is a 2speed fan, but for my direct wired application, it will be High and Off, no Low mode.