Guages on my car

A friend replaced my radiator cooling fan over the weekend for me and now when I crank the car all the gauges and the speedometer go all the way to the right, stay 2-3 seconds, fling themselves all the way back to the left, then assume their normal positions. Any ideas what he didn’t do right? Other than that, everyhting works fine and the car (an '03 Mustang) is running fine.

Your battery may be failing.