Posted on another forum and thought that this forum might be of some help as
well. Here is what was posted:

Was having problems with the thermal switch on the passenger side of engine
by firewall, bypassed that and now plugs cycle everytime. Not sure if I
should also replace controller, what do you think? Now next, because I have
had these difficulties with that switch, I have been turning the starter a
whole lot. Then when it turned, it turned pretty slowly, sometimes it
starts, sometimes it doesn't. Now, when I turn the key, I get nothing. No
light, no nothing. In fact if I turn the headlights on and try to start,
they don't even go dim. Man this is a pain in the ^&%. Can any assist with
this and/or supply me with some feedback? The starter was new about 14
months ago, the batteries (Megatrons), were new in Dec. of '04. Thanks much.

Oh, and this is on a '85 K5 Blazer with less than 100,000 miles on this
engine.

And to add insult to injury. Because it was having a hard time starting,
cranking real slow, the starter that is, I was curious if it was the
batteries reading low even though with a multi-meter it said almost 13
volts. Well I put a charger on it, one of those with 3 options, with one
being fast start and turned the engine (it did turn a little faster) and it
started. Shut it off, tried it again then nothing. Tried it again, then
something, maybe the starter made a loud sharp noise, and it started again.
Turned it off and then tried to start again, but got no lights or anything.
Can't even roll up the power windows. Kept trying and after a few times, it
managed to start one more time. I turned it off. Now when I turn the key on,
I got absolutely nothing except I can turn the lights on. Although I did
shift it from park to neutral and the dash lights flashed on really quick
only to go off again and not to come back on. What is going on here?!

Do I have a fried starter and ignition? Damn...this really sux!

Thanks for any help or suggestions you can provide. Might have to go to shop
on Monday!