etvchicago, I, like many here, have had starter problems with my Blazer. If you review my threads (many
), you'll see that I have asked the same questions you are asking. I have bought ebay Chinese starters, found my original (to me) starter was a 12volt Direct Drive, switched it out for a Chinese 24volt. Tested fine out of the vehicle, but I could not get it to turn over at all. The seller agreed to send me just the solenoid. The first one had purple wire issues that came from over tightening the connecting nut. It stripped and caused arcing that soon made starts hit-and-miss. The chinese starter worked fine for awhile. Got her towed home. By this time I had R&R'd the starter too many times and ended up modding the battery cable and the purple cable that go to the starter. Inline connecter were added to each permitting faster R&R times as there was only the brace and mounting bolts to deal with- no more monkey fingering the cable nuts.
Since I had the Chinese starter out- I decided to replace it with a Wilson starter. Ordered the 24 volt; 28MT Gear reduction type. Installed it and all was well. Then... it stopped. Under warranty I had it replaced. When I picked the new one up I noticed that the new one was identical to the old one but with a bright sticker that read "24 VOLTS". I may have installed the 12volt model even though I had ordered it for 24volts- their mistake. I had to put the Chinese one back in to get to the parts store that day, and it cranked up so well that I have never removed it to put the new Wilson one in (I keep it as my spare).
After all this, I get the feeling that the Blazer has wiring connectivity issues. I would check continuity of the purple wire that runs from the starter to the relay. If it looks good, clean the ends. The 24 volt starter cable is probably ok. Also have a look at the positioning of the ignition switch on the column. It may, through years of wear and tear, have slid to far forward and not make a sound connection when the key is turned- no start- or intermittent failures.
I know the starters from China suck; but we are having to many issues for the starters to be the sole culprit. Check the cable and connections. Run a new purple cable and label it "purple". Lastly, have a look in your fuse block for bad continuity.
Good luck.