push button for glow plugs and some switch?

[82K5_6.5L]

mounted underneath my steering wheel just a little bit is a push button, now the guy that i bought the truck from says its for the glow plugs..so what does that button do? i never push it? just wonderin? also next to this little push button is a flip on switch, when the guy put in the new 6.5L he added this switch, i have to flip it on/off to go into overdrive. plus i have to shift up, but when i shift up it says im in neutral but im not, its overdrive. why would it be like this?? i use it all the time and i know its for overdrive and all but y wouldnt i just be able to shift up? its like it is an old instrument cluster or something?? u guys know what i mean?? thanx

 

[AzzKicker]

The push button is to manual turn on the glow plugs. if your glow plug controller fails, you can still turn them on with the manual button. Or you can use it for colder weather etc.