I see this is a very old thread, however I just did this mod to my 02 SVT about a week ago now without seeing this thread. Then I tried to combine it with the mod to make a indicator light.
Once I got the speaker off, the connector posts were still in the circuit board. I decided to test the V's coming off of them just to make sure I had 12v. There was 12v there, however once I got the wires soldered on to the posts I suddenly no longer had 12v at the ends of the wires...?
At this point I removed the posts and tried just pushing small guage wire straight through the holes and soldering into place. This did not work either and I am still only seeing about .3-.4v out of the ends of the wires. The weird part about all of this is that my dome light ended up being deactivated and now it does not come on when I unlock the car or open the door.
I am using high grade electrical solder and good quality wire from a auto store. Not sure where to go with this now? Ideas anyone?