Step 5: Wire it all up and stuff it in a box
pin 0 - TX from the GPS
pins 3,4,5,6,7,8,9 - These connect straight across from the Arduino to the relay board/shield. Please note that you cannot use 2.54 mm spaced header as there is a gap on the Arduino between pins 7 and 8 and it just won't fit nice.
pin 3 goes to relay 8
pin 4 to relay 7
pin 5 to relay 6
pin 6 to relay 5
pin 7 to relay 4
pin 8 to relay 3
pin 9 to relay 2
pin 10 would have gone to relay 1 - but I blew that relay up on the first day (best to pay heed to the disclaimers)
pin 11 to select button
pin 12 to advance button
gnd - A connection to ground on the Arduino board is required to each of the two buttons and the GPS
5 volts - to vcc on the relay board
3.3 volts to power on the GPS
Power to the Arduino is +12 volts from a PC power supply
Power to the relay board is +5 volts from the PC power supply
At this point I jammed the whole mess into a small box I picked up at the dollar store. Had I been more patient I am sure I could have found a similar box filled with crap at the dollar store for the same price - but I opted for an empty one. The biggest reason for the box - to stop me from dropping my Arduino on top of any stray volts or wires.
The buttons that I haven't talked much about yet are just simple push buttons that release when you let go of them. one wire goes to ground, the other to the pin on the Arduino. I use the Arduinos built in pull up resistors so no extra parts required.
The 8-relay board had a jumper I disconnected so I could use external power. I tap 5 volts from the Arduino to VCC on the relay board and power the relay board with separate +5 and ground from an old computer power supply. The same supply I get 12 volts from to run the Arduino.