Problem: 3 doors (except driver) don't unlock sometimes (intermittent problem)
I think integral BCM powerlock relays don't work. I don't want to replace BCM, because it has theft programming in it (???).
So I decided to install 2 external relays to make locks work.
Opinions? Any electrical guys here?
I saw your post asking where to download the FSM for the 05 with a thumbnail of the door lock system. did you get the diagram for the 05 door lock system, and is that how you concluded that BCM is at fault?.
I don't exactly understand you attached thumbnail, but I get the idea.
Your idea of using 2 5 pin (SPDT) relays will work with the correct wiring to Lock/Unlock ALL doors at once(you say all actuators)
If you are willing to install an external switch, a DPDT spring loaded center OFF switch will accomplish that and eliminate the relays.
In addition you will need to know how much current each door lock motor takes to operate(Multiply by 4) to know what current rating you need for your relays(or Switch) contacts.
Also , I don't know if the motors are protected in any way(depressing lock or unlock for a long period of time) so thinking "worst case scenario"...
depending on how much current is drawn when all 4 motors operate, there could be arcing at the relay contacts (I don't know how much arcing a 12 v system will generate when switching an inductive load) that could potentially weld the contacts "closed" in which case you could burn the motors, so protect the supply side with a fuse.
You also mentioned that the condition is intermittent, are you doing anything to eliminate the possibility that both the original(Intermittent) and your "bypass" system don't operate at the same time and possibly conflict with each other?