true ignition circuit

We do GPS tracking and other similar things in semis and straight trucks...Most of what we install requires a true ignition connection...the problem...08 Freightliners have a databus ignition wire that we have been told not to interface with...we have found a wire per Freightliner schematics that we have been using but the voltage drops out while cranking...does anyone have a simple tip that would enable this wire to trigger something (relay, capacitor, etc) that would hold 12 volts while cranking...we have considered pulse timer modules, capacitiors, latching relays, but I know there are a lot of brilliant minds in here and I am just looking for some help...something fairly simple that one of our "trained monkeys" could handle.

What's coming out of the fuse boxes? I've used that method on M/Benz and Audi with data ignition switches. There always seems to be a live whilst cranking ign circuit at the fuse box.

This was actually covered just a few days ago- delayed off relay control

Thanks dualsport, I love it when you, "watersurgeon" and "I am an idiot" reply with your nice circuits which I shamelessly copy and file.

Shame on you Howie.

No shame, I'm the first to admit that if some one's got a better idea than me, I'll use it. That's not shameful it's resourceful. The very first thing vwe should teach youngsters in any walk is don't be afraid to ask.

There is a circuit in the fuse box that you can use. Unfortunately I can't remember what it is. Next time I'm working on a newer Freightliner I'll make sure I post up the wire color and location. It will save you some time and money compared to using the above relay circuit.Serving NY-NJ-CT-RI-MA-PA-NV

www.mobilefleets.com

Didn't I suggest the fuse box 2 weeks ago?  Doesn't anyone listen or go out and test anymore, or are you all waiting for OBD ll plug-ins?  For trivia's sake everything over here 7.5 tons and up runs 24volts, but some Scanias, Volvos and Mercs all have 12v+ perm and acc for the radio etc. The only "sleeper" circuits I've found so far on the trucks are on 44 ton Mercs and Renaults.