i have a 91 6.2 1/2 ton. i want to install a push button to manually control glow plugs. how would i go about that ?

i just did the same thing, went to autozone with $20 to spend and bought a starter relay "for a 1979 ford v8 pickup truck" and they gave me something that looked kind of like the electronic relay that came stock with my van, then in the electrical section i found a momentary starter push button switch and wired it up from the battery.
Just replace the two heavy wires on the stock relay and put them on the new one and put the new one it it's place and you should be done. One less worthless electronic gadget that can get you stranded somewhere.
Paul