Ok the card in your picture is the glow plug controller card. You do not need it if you are doing a pushbutton system.
Quick procedure to make a simple pushbutton glow plug system without 24V in the circuit:
Disconnect all small wires from the glow plug relay.
Disconnect the large red wire from the resistor block and reroute to the 12V terminal block located to the left of the master cylinder on the firewall. (If you do not have a resistor block, make a 10ga or heavier wire with two ring terminals that will go from the glow plug relay to the terminal block)
Make a small wire with two ring terminals on either end and connect it from the terminal block to one of the glow plug relay's small terminals
Make a long wire with a ring terminal on either end, connect one end to the glow plug relay's other small terminal and run it into the cab to where you are going to mount your switch. Make sure to grommet the hole in the firewall to protect the wire from chafing
Install your momentary switch in a convenient location under the dash
Connect your long wire to the switch
Make another wire that runs from the switch to a good ground.
Test the circuit, you should hear the relay clunk closed when you activate the switch.
To make the glow plug light come on when the glow plugs are active, splice into the dark blue wire in the glow plug harness and connect it to the same side of the switch as the glow plug relay wire.
That's it, easy peasy...
Later,
Joe