Now this is our little shop runner not my blazer but its similar enough I figured I'd ask so as to maby get an idea of something I possibly missed.
The info: 1997 2wd s10 cab&1/2 4.3 auto.
The original issue: it needed a heater core and while the dash was out (it was in horrible shape) it got replaced.
The problem: after changeover (donor dash was from a 97 4x4 blazer) the brake warning light is dimly lit, no blower motor, and the power windows don't work. I used the correct cluster that matched the truck originally (wasn't giving up my 200k mileage) but the donor dash wiring as the original had some half-fast hacking in the radio harness. Did I miss something possibly or am I pulling the dash back out (not that I mind that) and switching harnesses?

 

Are you sure that you connected everything all the way? It seems like a pretty common problem I see on this site after someone replaces a heater core that they have some sort of electrical problem, and have to back over everything a second time.

 

Enforce bolting it down I 2nd guessed myself and slid it back forward (because I DID forget to put the antenna wire through at first) so I doubled over all plugs before the boltdown. (I look down on no suggestions feel free no matter how trivial it may sound)

 

Problem solved, I had to switch harnesses so the one from the truck was in the new dash and everything is back to normal. So useful information, don't ditch your old harness!

 

Thanks for posting your solution. It drives me nuts when someone fixes something, and just posts "I fixed it" and that is that.
Glad you got it figured out.

 

Yea "it's fixed" ain't a helpful solution and bothers me just finding it as an answer when I hunt a problem.