timed 12v relay for power folding steps

So I want to start with I have little to no experience with relays and making them work for the functions I need them to do oustide just replacing / installing them after somebody else already did all the programming work. I am looking to do a retro fit on some power running boards on my Escalade that did not come with them from the factory. Because mine did not come with them from the factory I have to figure out how to control them myself, rather than the on board computer. One good thing is I know the color wiring diagram for the motors and it's function, as well as the door open / close trigger wires inside the factory harness. So here is my issue, I need to find a relay that can perform the following function:

Must have constant 12V power; once the door open trigger sends the signal to the relay I need the relay to allow 12v power to flow to the motor extension wire for 3 seconds and then stop. *the motors don't have stops therefore if a constant power was applied the motor would continually run even though the step would be fully deployed and eventually burn up*. Inversely, once the door close trigger sends the signal to the relay I need the relay to allow 12v power to flow to the motor retraction wire for 3 seconds and the stop. I have also been advised I should "diode" the relays so the 12v constant doesn't send feedback through the "door open / close trigger wires", not sure what this means exactly.

I put together the following diagram sketch of how I think it could possibly work

[IMG]https://img.photobucket.com/albums/v359/baggedLVintegra/RetrofitPowerRunningBoardSchematic.png[/IMG]

Does anybody have any experience with this type of application and/or timed relay experience and could point me in the right direction of where I could purchase a relay to perform these functions?

Any help is GREATLY appreciated. Thanks - Josh

sorry the image embeddment didn't work, here it is

Interesting project.  It looks very do-able.  The 3 second driver relay output is the challange.

While it might be possible with some sort of R/C control circuit to give the 3 second timinganother more logical and direct method to accomplish this would be with four 30/40 Amprelays and 4 PAC TR-7 modules.  Each TR-7 would monitor one door trigger and control onerelay.  The relay wiring would be very simple and you could make up a small enclosure box for each folding step, one for the right and one for the left.  Here is a link to the PAC-TR7module.   https://www.the12volt.com/installbay/file.asp?ID=1031

Relay wiring - Pass side:

Relay 1 = RetractPin 85 to TR-7 #1 (-) White Output set @ 3 secondsPin 86 and 87 to +12V constant fused @ Step motor needsPin 30 to Step Motor Dark BluePin 87A not used - insulate

Relay 2 = Extend

Pin 85 to TR-7 #2 (-) Output Output set @ 3 secondsPin 86 and 87 to +12V constant fused @ Step motor needsPin 30 to Step Motor Dark GreenPin 87A not used - insulate

Both TR-7's would be programmed as Feature #15, one input pulse gives a 3 second output pulse.

TR-7 #1 RetractBlack to Chassis GroundRed to +12V thru ON/OFF control switchBrown to (-) Light Green door close triggerWhite to Relay 1 Pin 85

TR-7 #2 Extend

Black to Chassis GroundRed to +12V thru ON/OFF control switchBrown to (-) GREEN/ Black door open triggerWhite to Relay 2 Pin 85

I imagine there are less expensive ways to do this, so hopefully someone else can jump in with

another idea.

Soldering is fun!

So the scenario you lay out above is just for the passenger side only right? So it would need to be doubled and would require (4) total relays and (4) total PAC TR-7s?

Sorry just re-read the post and it answered my question, made more sense the third time through :)....so yeah that's a bit pricey, which I don't mind if that is what HAS TO HAPPEN to make it work, but will entertain any ideas

Yes, that is correct.  One set-up like that for each sides' folding step.  Total cost about $85 with fuses, etc but you can control the relays output to the second.Soldering is fun!

So I'm pretty sure I comprehend your whole scenario and it seems that it would function exactly how I intend, however I am confused by the trigger input / output of the TR-7 being a negative? Wouldn't the door open trigger signal from the vehicle be outputing as a positive? Or am I confused? I have not actually tested to know, but you are much more experienced than I and may possibly already know

Good point.  You didn't mention the Escalade's year and I just assumed (-), but that is thebeauty of the PAC TR-7.  If you find that it is a (+) trigger you can use the TR-7's Green (+)Input trigger wire instead of the Brown wire listed above.Soldering is fun!

Ok I assumed that was a no biggie, but just trying to grasp everything....I greatly appreciate the help. The Escalade is an 07 BTW, attached is the factory power running board wiring schematic and then also aftermarket AMP power step wiring diagram that shows the trigger wires to tap into for the desired functions.

link to amp power steps installation instructions

http://www.amp-research.com/wp-content/uploads/2010/05/download_btn.jpg

they need an edit post button lol it won't let me add the pdf but if you go to 07+ Escalade download on this page you can see it http://www.amp-research.com/products/truckaccessories/powerstep/