diesel overdrive light

the over drive light on my 92 f-350 started flashing awhile back, flashed for a couple of days, then quit working. overdrive works fine, engages and disengages fine just no indicator light. any help would be greatly appreciated. the truck is a 92 f-350 7.3L, automatic overdrive transmission, with 485,000 miles. also looking for any performance upgrades considering banks sidewinder not sure of other options though