Just picked up a 2005 Mustang for my son yesterday and the coolant temp gauge doesn't work. Looks like it's a very common problem with the stepper motors used on the instrument cluster. replacing the instrument cluster is very $$$, Think I can send it off for repair or possibly unsolder/resolder new parts on but it sounds like the gauge is basically no more than an idiot light anyway. got me thinking of other possible options. started with just a "real" aftermarket temp gauge, then something like a scangauge or dashhawk. Finally ran across an UltraGauge here...
http://www.ultra-gauge.com/ultragauge/index.htm
Plugs into the OBDII port and looks like it's got a lot of functionality for only $69. Being able to set Alerts is really nice, i.e. can set to sound an audible alert if the coolant temp exceeds a certain temp, among other things. Also has the added benefit that it works on any car with an OBDII connector so I could easily move it between cars if I wanted.
Anybody know anything about them or have other suggestions?