If the 2004 is like the other PDM, it is not a true plug and play. The kit requires the old main and power harness to be removed and new one installed which comes with kit.
That said, the new harness does plug directly into the existing connector of components (lights, switches, alarms, etc.). Still just be aware you will have to remove the current harnesses with exception of the separate one going from ignition module to coil and starter switch.
One nice thing with the PDM is that you do get a complete new harness and if for some reason the problem one has that may cause for the change was due to say bad or chaffed wire in harness that caused EHC or makes one think EHC, that problem will be taken care of with PDM (assuming one takes the time and does not mess up the new harness of the PDM when installing).
A WP used (most likely still does)to require that one had to cut the connector going to EHC and splice in new one for the WP, should not be an issue if one takes their time and does the splicing and connections right. Still there is chance for improperly crimped pins, dry sockets from solder, mislanded pins, etc. So taking time, doing things right and confirming all splices, pin connector, solder joints (if one does such) should not be a big issue.
PDM is easier, but some of the same issue with bad pins, mislanded pin, bad solder, etc can occur with PDM if bad from factory, just decrease much if BDPP or their vendor uses good QC and test before sending out.
