Overdrive on/off light

I have recently had my odometer/speedometer head replaced on my '95 Ranger with 87k on it. However, now the OD on/off dash light does not come on, but the overdrive and everything else seems to work fine. Not sure what wire, or fuse to check as manual is vague. What has my mechanic done or not done or is something else amiss?

Could just be a blown out bulb. Take it back and describe the problem.