You have three options:
1) Use Don's method above.
2) Tap into the battery behind the disconnect switch. Dodge tells you to disconnect the ground, but when I install on these types of vehicles, I move the disconnect switch from the ground terminal to the positive terminal. Then I hook it up in this order: Battery (+), SMI power, disconnect switch, original battery cable. In this case, the brake lights of the Dakota would still be inoperable. For your SilentPartner, tap transmitter red wire into the blue wire that goes from unit to the breakaway switch instead of the brake-light switch. *This is the method I usually use.
3) Use a portable power jumper to power your SMI system. In this case, you would still need to tap-in to the blue wire as in the second option.
Feel free to write or call me for any additional information.
Research and Development
SMI Manufacturing, Inc.
P.O. Box 14040