Disconnect power to accessory

The link you posted didn't show anything so I will give you a suggestion. Take the ignition input wire from the unit and cut it. connect the wire coming from the doorlock speed control unit to terminal 87 (the center pin) of the relay. (SPDT of course). connect the other side (the side going to ignition) to terminal 30 and jump another wire from 30 to terminal 86. (this will supply 12v to the relay coil when the vehicle is on and the door is open) connect the passenger door domelight wire to terminal 85. How it should work is when the door is closed the relay is not activated so 30 and 87 are connected and everything works as normal. Once the passenger door is open the domelight control wire from the passenger door will send negative to 85, activate the relay and open the circuit so effectivly the doorlock speed control module will think the ignition is turned off. Once the door is closed the relay goes back to its "at rest" state reconnecting the ignition wire where it will operate normally again. Let me know if this works. Good Luck

CORRECTION: I made a boo boo, but forgive me, its late. The center terminal of the relay is 87a, not 87. With this circuit DO NOT use terminal 87. Also make sure you insulate terminal 87 since when the door is close the 12volt ignition will be resting on 87. If it touches ground we have a problem, which is also why I am going to reccomend to fuse the circuit. Cheap insurance as a 25 cent fuse is alot cheaper then fire damage repair. What I do for extra safety is put a connector on 87 and then tape the whole thing with quality electrical tape, then put a zip tie around it so the tape will not unravel. Then mount the relay somewhere safe and away from moving parts with another zip tie. Sounds like overkill but better safe then sorry. I have been in the business a long time and have seen my share of disasters, all of which were easily avoidable.