Measure for the lengths of the wires by doing a trial installation. Cut them all the same length and then trim them just before soldering. Twist together the 4 red wires so that their resister nets are in parallel. Ditto for the 2 yellows. Put a piece of tape over the wire as it comes over the edge of the box.
More Testing Hook it up to a battery and test.
The resisters should get reasonably hot but not so much as to damage the foam or smell bad. This is a good chance to play around with your meter and measure the current draw. Such is life. If we really cared about precise power levels we could use a regulated power supply but this is just a heater, after all. Final Installation Remove the backing from the weather stripping and install the ring around the edge of the corrector plate mounting ring.