power door locks, diode isolate?

Sorry, been a very long day, and I have a killer migraine. Should have said:- Actually NOT correct or only partially so, yes they are there to "condition" the polarity or as Coolen's rather good analogy "one way valves. The problem is with the latest cars working the locks through BCModules, you can get all sorts of feedback from the module, I've had this problem with BMWs, Euro Fords and Euro GM, on the GM the unlock trigger wire which was neg going was showing a constant neg, I had to diode this as the alarm's locking wouldn't work. As I said before, if you have a 6 wire (i.e. relay driven) lock output, it doesn't matter, if you have a 2 wire neg. or pos. then diode it just like you would a relay.

Ok, so if I'm understanding this correctly, if a vehicle has a "flip flop" type circuit to lock/unlock the doors (+ lock/- unlock), I should use diodes? But if the R/S system had a pos output for lock, and a neg output for unlock, no diodes needed? And if the R/S only had neg outputs for both, use a relay to convert the polarity and no diodes? My next vehicle will be an 03 dakota, and according to the wiring info, the same wire locks and unlocks the vehicle. This is a (-) signal. So how does that work? When the truck sees a - it will lock, and when it sees it again, it unlocks? These connections are to be made at the CTM, since the locking system goes through that, do I diode that? Or am I ok since the prostart unit I'll be using has neg outputs? Thanks once again everyone, this seems to be coming together well

I think you're getting the wrong end of the stick! Please actually read my posts. The diodes are there to protect the vehicle's BCM AND the alarm-R/S. As for the Dakota, you MUST use relays or a unit with relay driven outputs, place a resistor in front of a two wire and you won't have enough current to operate the locks.

Thanks for your reply, and I am reading your posts. For this vehicle I'm ordering an idatalink module and be done with it. I'll continue to research this information before I attempt any of it. I want to get a good grasp on diodes before I worry too much about resistors and such. I think I have it. These diodes are only needed when the locks are operated through the BCM. Which would be identified within the vehicle wiring database. Correct? If within the data base for whatever vehicle, there is no mention of locks going through the BCM, isolation is not needed. Correct? Thanks again

Yes. In this line of business, diodes are used as "an anti feedback" device just as you thought, no hidden meaning here but you are protecting your components, think relays and the advice to place a diode across the coil.

Even come across this in car audio, add a Bluetooth kit to some VWs and Euro GM (their wiring is effectively the same), and the locks won't work! There is a capacitance holding a charge in the car kit, this feeds back down the ACC lead, this tells the BCM, "oh look my user has left a key in the ignition". You have to diode block the ACC to the car kit!