Fuel Idiot Light not working.., what gives? Options

[Literati914]

I know you can take the sending unit apart to clean terminal on the top part (I've searched and read through old posts) but nobody has mentioned if corrosion at the bottom on the sending unit causes the idiot light not to work, and mine ain't working (IMG:style_emoticons/default/headbang.gif) . I'm trying to use an simple two terminal aftermarket external "red" push-in type light that I've installed in my dash (not using the stock Fuel gauge, it's a smaller VDO unit though). I've got the black wire from the fuel tank sender going to one side of it and a ground wire going to the other but it's not coming on.... so I assume there's a problem with my sending unit. Would like to take it apart and save myself $100 if possible.

Doug C