Normally, if both the car owner and target have hardwired then it is like neither have anything. Like stopping power and standard juggy. Both cancel each other out.
One thing I've done that can be effective against cars is to carry your EMP mine in reserve or if you throw it keep it relatively near. If you get the message that one is coming stand in the middle of it or pick it up, move to a safer location if needed, and throw it again at your feet. Most of the time the mine will kill the car before the owners triggers it. Owners with Hardwired ignore the mine. Originally hardwired didnt transfer to the car but people didnt like that because everybody was running around with hardwired.
Car jamming and such has gone through several iterations to find one that works. Before it stopped the car dead in its tracks. The owner could do nothing until the enemy player moved away. So all a player has to do was stand there and EMP nade the thing to kill it. But that wasnt overly popular either.