If the door switch can activate the relays in the DLM that is enough for the DLM to operate the solenoids. If the DLM can't activate both solenoids properly the problem is further "down the chain" than the switch that initiates the process. Manually pressing the relay isn't definitive because you are still using the contacts in the relay. It is possible the solenoid he put into the passenger door is no good so the best test would be to put in a known good one which is in the driver's door. I agree it is a lot of work but it will tell you what is wrong. I hate buying parts to "throw" at a problem and in the process not actually fixing it but R & R ing a lot of good parts. It is wasteful and worse, you disturb things so by the time you are done you may have introduced more problems than you are fixing. I much prefer to troubleshoot and diagnose instead of "shotgunning" by throwing parts at a problem till you get lucky. When the Central Locking System is not working well the best thing to do is to go over ALL of the adjustments in BOTH doors to get it to work correctly. It also doesn't hurt to clean and lubricate all of the mechanisms.