Please verify my Dreamcast to Arcade Controls wiring (I dont want to ruin $300)

[sofakng]

I'm wiring up two Dreamcast controllers and an IPAC/2 to my arcade controls.  Here is my proposed wiring scheme:

DB25 connector for Arcade Controls (P1 and P2)
1 - Up
2 - Down
3 - Left
4 - Right
5 - B1
6 - B2
7 - B3
8 - --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type--
9 - B5
10 - B6
11 - Start
12 - Coin Button AND Coin Door mech
13 - GND (This GND is connected to ALL buttons *AND* my coin door mech GND *AND* my P360 GND)
14 - +5V input for P360
15 - B7
16 - B8

DB25 for each Dreamcast controller
1 - Up
2 - Down
3 - Left
4 - Right
5 - B1
6 - B2
7 - B3
8 - --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type--
9 - B5
10 - B6
11 - Start
12 - (empty)
13 - GND
14 - +5V
15 - (none)
16 - (none)

Each DB25 connector for the I/PAC2 will basically be the same layout as the Arcade controls DB25 except I'm very confused on where to get the +5V from. 

I've been using my Opti-Pac to get a +5V for the P360, but now that I'm hooking up my Dreamcast I'm confused on how I should be setting everything up...  I know I need to seperate GNDs, but I was told that I shouldn't get the +5V from my Opti-Pac and then GND it to something else BESIDES the Opti-Pac.  (eg. if I connect all the GNDs for the buttons and coin door, then do I also connect the GND from the P360 but get the +5V from the Opti-Pac?)

I'm sorry if this is confusing.  It's just that I'm really worried about frying my P360s or my IPAC/2 or my Dreamcast...

Please help... :\

[Minwah]

How about have a completely separate cable for power, and get +5v from a PC drive power connector - you don't have to worry about that part then - it'll be powered regardless of whether DC / IPAC is plugged in.

[Dave_K.]

How about have a completely separate cable for power, and get +5v from a PC drive power connector - you don't have to worry about that part then - it'll be powered regardless of whether DC / IPAC is plugged in.

Yeah, but the problem would be when the p360's are powered by the pc power, and the sticks are connected to the Dreamcast, and he says he is sharing the grounds between buttons and P360.  Poof!

You can get +5 from each respective dreamcast pad.  So I don't see a problem.  Your grounds and +5 will all go to the DC when DC is plugged in, and when your PC/Ipac is plugged in, it will all go to the PC.

To get power from the DC pads, use a multimeter and check the blue wire coming in from the game port to the pad pcb.  According to this diagram its pin 2 on the internal pcb connector (inside the pad).
http://mc.pp.se/dc/controller.html

[sofakng]

Ok, so are you saying that the I/PAC2 DB25 cable should be wired like this:

1 - Up
2 - Down
3 - Left
4 - Right
5 - B1
6 - B2
7 - B3
8 - --BINGO! Either that, or I was attempting to say "before" but it was too many letters to type--
9 - B5
10 - B6
11 - Start
12 - Coin Door *AND* Coin Button
13 - GND (This will be the GND from all buttons, coin door mech, and GND from a 4-pin PSU cable, and will connect to the IPAC/2 GND)
14 - +5V from a PC 4-pin PSU cable?
15 - B7
16 - B8

[Minwah]

Yeah, but the problem would be when the p360's are powered by the pc power, and the sticks are connected to the Dreamcast, and he says he is sharing the grounds between buttons and P360.  Poof!

Sorry, I meant get a separate ground from the PC power supply only for the P360 power.  Then use the GND from the DC controllers / IPAC for the controls.