power door locks, diode isolate?

I have always wondered how one would know whether or not they'd have to diode isolate the locks? I've read the diodes section and the door locks...maybe I'm just missing something obvious here. I know that diodes serve as 1 way check valves, but what I can't seem to grasp is identifying when to use them.

Under the vehicle wiring section of this site for example....if there is no mention of diode isolating whatever, does that typically mean that there is no requirement? I've just noticed that some information states whether or not diodes are required and where. I just needed some clarification on that.

Being on the subject of power door locks, is it just as simple as using the r/s's lock/unlock wires to perform that feature unless otherwise stated in wiring information?

Thanks in advance.

Two wire lock outputs as distinct from relay driven 6 wire outputs may be flip flop, i.e. pos or neg. Some BCM units on the cars are extremely sensitive to this, i.e. polarity conscious, hence the use of diodes in the way you suggested. also prevents feedback from the BCM damaging the alarm or R/S.
Don't understand what are you getting at with the last part? Do you mean adding actuators?

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Thanks for the reply.

Basically what I'm trying to figure out is how I can I identify the need for diodes in a remote start system when it comes to getting the power door locks to work. As in how do I know what vehicles require this isolation?

Thanks

Are you an installer or do you just want info for a particular vehicle?

As a matter of correct procedure always use them when a unit has flip-flop low current lock outputs.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I do installations of emergency warning equipment, and I'm just starting to get into remote starters. So when you say use diodes on low current lock outputs- just so we're clear, use them when a vehicle has a neg lock system?

In my world of wiring, active high is positive, and active low is neg. Is this what you are referring to?

Thanks!!

Specifically, some DEI Viper systems have door lock outputs as shown below :

Door lock harness, 3-pin connector
1 BLUE      (+) LOCK     (-) UNLOCK OUTPUT
2 EMPTY NOT USED
3 GREEN    (-) LOCK     (+) UNLOCK OUTPUT

These outputs flip / flop between the two polarities (+) and (-).  As Howard pointed out, if you are connecting these type outputs to a vehicle that requires a low current (-) pulse, it is best to add a diode in the output wire so that the vehicle only sees the (-) going pulse and blocking the (+) pulse from affecting the cars delicate BCM circuitry.

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Soldering is fun!

Ok, things are starting to get a bit more clearer. So if a vehicle takes a neg to lock and unlock, and the r\s has a neg output for lock and unlock, I wouldn't need a diode? Only if the vehicle takes a neg and pos to lock and unlock? I have installed prostarts before, and if I remember correctly they have both options as far as lock outputs are concerned.....I think.

Thank you

Correct.  If the vehicle requires a (-) pulse for the door lock / unlock wires (  known as Type B ) and the remote starter only has a (-) output ( like Ultra Start or Compustar units ) then you could connect directly to the vehicle.  If the remote start unit has the flip flop type outputs ( like some DEI units ) then diodes would be advisable.

Some remote start units ( like Bulldog ) have built in relays and allow you to choose the door lock relay oputputs by inputting a (+) or (-) to the relays. 

There is a section on Door Locks on this site that has some good info on this subject.  Also, most better quality remote start install guides have a section on testing and wiring for the various types of door lock systems found in vehicles.

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Soldering is fun!

Actually NOT correct if 2 wire lock outputs

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

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.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

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.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

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.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

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!

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.