Engine won't turn off

[rlux4]

It hasn't been my experience that a dual relay goes bad any more often than any electrical component. That is unless you're working above the starter and drop a wrench onto the hot wire on the solenoid without first disconnecting the battery. There's a heavy gauge brown wire that runs directly from the battery to the dual relay and the short has a direct path to it. This can fry a dual relay.
I keep a spare of all of the FI components just in case one goes bad and this way if I need it right away I don't have to wait for shipping. You can usually get pretty good deals on these parts from fellow members doing part-outs.
As far as replacing it, there's a good diagnostics for it here:
http://www.wcmotors.com/personal/Fiat%2 ... agnostics/
It's easy to test and if it's working properly there's really no need to replace it.
What I've found is that it's bypassed by a PO not because it failed, but because they were unaware of the inline fuse that supplies one of the 12V sources to it, or they couldn't find the fuse holder behind the main fuse panel.
Ron