Ignition woes - switch needed?

[GMCNUT]

I don't know why, but when its cold or started for the first time, my 72 blazer ignition has started hanging when I hit the key and the starter will turn over and over and over a thousand times unless the motor starts or I disco the battery. When hot, its started deciding not to crank at all - flip the switch and nothing happens like its totally disconnected from power. After it cools down, seems to start fine. Assumed at first this was a starter solenoid issue, so I replaced that with a brand new one only to see it act the very same. So turned my attention to the ignition switch and replaced it with a same switch spare I had laying around from a junk yard truck, and it is still doing the same thing. So I assume the junkyard ignition switch was as bad as the one I swapped it out with? New solenoid? Can't be the starter itself I would't think because it waits for the ignition to be turned on to make the solenoid jump out - the solenoid would work regardless of the starter working and thats not occurring so it has to be the switch itself - right?
So, assuming all of you agree the switch must be as bad as the one I removed, Ebay shows about 10 different ignition switches and each seller claims their switch is correct for 67-72 - part numbers I see are:
1116695, 1116704, 1116688, 1116711 and on and on. Does anyone really know what GM part # the ignition switch is supposed to be for a 72 Blazer w/ normal 350 V8 / Automatic / CST / etc?

[DeadheadNM]

This looks like the real deal here: http://67-72chevytrucks.com/vboard/s...d.php?t=787220

[A1971Blazer]

be sure to check the connector that plugs into the switch...it can short in there and cause the starter to run on like you are describing..the purple wire is what energizes the solenoid...check it for a short as well....could be shorting intermittently in that circuit...