Use the black wire as it is- it's going to the switch, so when is sees pressure it goes to ground. Use the white wire from the solenoid as the +12v feed.
I'd still hook that switch to an air source and see where it closes. It really needs to be at 40PSI or a little over so you don't get a shudder if it comes on to early. It seems to work out the 4th gear pressure that switch sees is close enough to 1:1 with road speed- 40PSI=40 MPH
Last edited by TimAT; 09-21-2010 at 12:22 AM.