I have found several different schematic for building your own interface cable, how do i know which one would be th best for me and work with my applications? what I have is an 1227747 ecm with the asdu prom id. here's the different cable schematics i found. Which one the right one for me? http://winaldl.joby.se/aldlcable.htm or this one http://www.home.aone.net.au/~techedge/vehicle/2tran.gif Any help would be greatly appreciated thanks,

Either one is fine for a TBI computer. If you use the first circuit do not us R3 or R4.

So I don't need to use the one with the seperate power? What about using the one with the 2 transistors? It has the pinouts for a DB25 parallel port which my laptop has, would this configuration work? Has anyone tried this one?

I would recommend at least starting with the separate power to get it working. Then you can try changing it to using power from the serial port to see if your laptop will support this. I do not think tbi requires the 2 transistor. Will work fine with tbi but the second transistor is used for other ecm types that need to be sent characters to change mode.
The 25 pinout is for a 25 pin serial port, NOT parallel port. The 2 transistor with 9 pin serial port is what I use.