1978 240D
I think my problem is in the ignition switch. Sometimes the glow plugs work and sometimes not. Sometime I rap the steering wheel and they come on. I went and bought a 15 amp push button switch yesterday, but I would sure like some directions on which wire to feed raw power and install the switch.

 

Push switch gives you little knowledge about required timing for glow plugs. Those plugs can take a minute of power, but at some time they'll burn. I would rather spend some time and restore original wiring.
If you really want to install the push switch, the easiest way I see is come with the wires from the relay, that is easily accessible under the hood.
Did you make sure all the fuses are copper? Just a tough.

 

If you were to use a switch to bypass the unit, You will need at least a 40Amp switch, and some pretty thick wire. Or else keep a fire extinguisher handy