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?

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.

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.

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.

Soldering is fun!

Actually NOT correct if 2 wire lock outputs