2004 Ford Focus • 12,000 miles

I own the wagon version (ZTW) with 2.3L engine. After my original Motorcraft battery finally died recently (it lasted 8 YEARS. UNBELIEVABLE!) I purchased a new battery, the exact same Motorcraft battery that was in the Focus when purchased new (BXT-40R). After installing the new battery and driving it around town at night, I noticed that the dashboard instruments intermitently fail. That is to say that fuel gauge shows my car is empty even though I just filled it up with gas. The speedometer reads 0 no matter what speed I'm actually traveling. Most of the gauges read incorrect values, BUT as I said before, these problems come and then go away quickly. What do you think the problem(s) are and do you think that I could fix this myself (I grew up in the car business and am an avid do-it-yourselfer)?
November 8, 2012.

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