Any solutions to one wire car door sensors.

[Hibrydsoul]

how do I work around only having one wire coming from the door sensor to wire such devices as a car alarm which have two wires for said door + and - ?

[HONDA spoilboy]

Put the + on a direct supply to the positive on the battery
Use the one wire on the door switches as the ground -
Make sure there is no other ground wire or connection to the - wire