So you want the Diode to stop backfeed to the switch/LED?
This should do fine, I would think: http://www.radioshack.com/product/in...entPage=search
You aren't putting more than a few milliamps through the wire to the solenoid (from the switch) right? If it's less than an amp, then that should do fine. I have used them before for various things, mostly including remote starters.