That's a non-user-replaceable item. Mine went out a few months ago too. I called SPA (317 271 7951) and they warrantied it for me. I was told that they had a bad batch of backlights for the LCDs and they've since remedied the problem.
The dealings with SPA we're good/bad. I had the option of either sending mine in for replacement, or they'd take my card # and send me a replacement and then credit the card when they got my defective gauge. The good: I got the gauge in a day (they're 100 miles south of me). The bad: it took them 3 months to credit the money back to my card after they recieved my defective gauge. I sent them a handful of freindly reminders via email and was sent a "you should see it this week" reply each time. At the end of the 3rd month I told him it would take it up with my credit card company and the credit showed up the next day.
So, they will take care of you. But watch 'em if you take the route that I did...