Adding Retained Accessory Power, RAP

GM vehicles have RAP which allows for the radio to be on in the car for up to ten minutes after the key is turned off. Once the door opens, the RAP is disabled shutting off the stereo. I want to add this type of function to my 2005 Lexus RS330. I am curious if there is any type of timer relay that may be easier to install. One of the methods I was thinking was just using one relay as follows: Pin 85& 86 (coil of relay) Pin 30 & 87 (Relay Switch) Hook pin 85 to Key On Power Hook Pin 86 to ground that is disrupted by door jamb switch. Pin 30 to battery feed Pin 87 to stereo AND back to Pin 85 (keeping the relay coil powered even after key is turned off) Since Pin 87 is also feeding pin 85, once the relay is cycled on, it will remain on indefinitely. By having the relay Negative (Pin 86) switched off by the door jamb switch, that would disrupt the current feed from Pin 87 back to Pin 85 thus shutting off the relay even when the door is closed. Bad part of this method is there is no time out timer. Will also need to install a diode so only the radio is powered by the relay and not the fan blower circuit for example. Is there another method that may work better for what I am trying to accomplish?

Have a look at the DEI 528T Pulse Timer Relay.

Thanks OldSpark, but that timer is only good for 10 seconds. I looked up Rap Module on google and I found on a gm site this diagram that links back to here...The12volt.com. It is a diagram that shows what I was trying to state in my initial post. I also found where the RAP module can be removed from a camaro or firebird and I will try to find one from a junkyard. Here is the link I found that is interesting: http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20110502-2-102130.html

You could build your own 555 timer circuit tho I understand the DEI 528T is based on a 555 so it may be easier to modify that (increase the timing capacitor size). Otherwise there are various timer circuits available as kits, tho I choose to build my own with the exception of the DEI 528T. (Not that I have bought one yet, but I considered it cheap enough to warrant avoidance of DIY resources.) I haven't investigated the logic you propose - I'll leave that to others ((ie, switching & control). But re that, and the "interesting" link you provided, I've always had my radio/HU powered direct from the battery, tho recently I did involve my IGN circuit due to the high drain (~130mA) when off with both constant and switched supplies at +12V (due to newer USB etc inputs). In that case I rigged an ignition (tho normally that would be be ACC) actuated relay which latched on using the HU's remote output, hence requiring IGN (else ACC) to enable the HU to be switched on but it then stayed on until I turned it off. (The relay connected my heavy fused battery constant to the HU's switched power input.) I was going to add a switch to enable ON without IGN; or OFF when IGN turns off as well as my default ON with IGN but manual off. If I were to add a timer function, I would have used a PICAXE 08M2 since it's almost as cheap as a 555 timer but fully programmable (no caps or resistors to change), but in part that was due to a similar function for my dash mounted 3-digit voltmeter. (That used an IGN actuated PCB relay to connect its +12V direct to battery +12V, but likewise that was later intended to have an on anytime as well as a timed option - ie, stay on for 2 minutes after IGN off, or 2 minutes after a momentary on anytime switch actuation.) When I fitted electric windows to the same 49 year old vehicle I used a constant supply. Likewise that was to have an added lock (deactivate) switch and IGN-only option, possibly with timer (eg, can open or close up to say 2 minutes after IGN off) similar to above but also with and auto-open & auto-close (and safety) feature using current sensing, and a (default) delayed auto-close after IGN off. Apols for the rant but I'm showing my preference for "always available" accessories like HUs, windows, wipers, some monitoring, camera recording etc, else that they be user selectable despite their OEM or default IGN/ACC powering. And the PICAXE comes in due to its "one circuit fits all" - only the program varies (unless I use a universal program with automated sensing else some user configured component/switch that determines its application) - plus that it only uses ~14uA in full operation as opposed to the 10mA standby or idling current of a 555 timer (that's very important for solar applications like trackers and monitors, or long term unused-vehicle applications).