my 2010 F-150 Tachometer indicator arm does not illuminate when the lights are on. how would I fix this issue?

I have a similar problem in my 2005 Ford Five Hundred with the speedometer, just about one half of the gauge illuminate and cant see the red speed indicator in that area. Small bulbs are position to give light to the gauges and in my car, and possibly in your truck too, one burned out. The cluster must be removed to replace the bulb, in the F150 I think it is not too difficult but does take time and patience. In my case, it is a more complicated operation and, frankly, I decided to leave it as is. Be careful when removing the parts, remember they are plastic and the attaching hooks can break easy. If you go online, I am sure that you will find videos showing you the correct procedure to do it.

Thanks for your input Jorge, but the all the gauges appear to be back lit and only the tach's red indicator arm doesn't illuminate the the numbers do in white also back lit. and the three small gauges right above the tach appear normal and fine.

That is because the needles have a reflective coat of paint and maybe the one in your tachometer has faded. By the way, the needles are clear and the paint is applied on the back.

thanks again for your input, But in my 2010 F-150 none of the needles on any of the gauges are clear with paint applied to the back, and it didn't fade away, one night it just went dark, as in no light source. but only at night the one needle is dark as it moves over the illuminated white numbers, it even blocks them out a bit. During daylight it is just as red as the rest of the other needles in the panel. So thanks again for all your help, if I ever get a 2005 Ford Five Hundred it may even come in handy :)