Heaater A/C fan motors wont blow

I have a GMC Sierra 1500 4 wd extended cab pickup. My blower motors were working fine. I shut them down when I parked the truck. I left again approx. 10 min. later, and there was no air blowing when I turned them on.
I have checked all the fuses I can find, fuse block under hood and in the truck. cant tell which relays are to what under the dash, as my over the counter chiltons has no really good diagrams etc. I tried to find a expanded schematic to no avail. I have had not much luck getting to view any pictures etc of the heater, A/C blower circuits. Can anyone help out with info on similar problems, or with a good schematic, and maybe some pictures too?
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Year and engine?
Steve

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1996 5.7 liters. I have now experienced an intermitent problem. The fan motors just came on while I was driving. TYhey would onluy work on High. The other 2 speeds were no go. If you turned the switch off it would allow the motors to restart again when turned on. There is a relay behind the glove box, and there are 2 different wire connections. My problem lies in one of these two. IThe connector that has multi wires and colrs in it seems to maybe be the one. But it goes through the firewall on the pass. side as does the other connection too. That one has 3 wires , a red and 2 blck. They seem to be really stiuff and are like this about 1 - 2 inches fron the connectoer. These didnt seem to get the bloweers going again, just the onew with the multi wires in it. The colors were grey white green purple and I think it was maybe brown. But moving this seems to have started the ball game agAIN. hAVE YOU HAVE THIS KIND OF PROBLEM BEFORE ETC. tHANKS.
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Oh my...

allow
<nonsense snipped>
From Mitchell verbatum (almost):
If blower motor runs in High only:
Turn ignition on, set blower to LO. Remove high blower relay from socket, located under instrument panel on top of A/C heater case. Connect test light between high blower relay socket DARK BLUE wire and ground. If test light glows, replace high blower relay.
If not, disconnect front blower resistor, located under right side of instrument panel on A/C heater plenum. Connect self-powered test light to DARK BLUE wire between front blower resistor and high blower relay. If test light glows, replace front blower resistor. If it does not, repair open in DARK BLUE wire between high blower relay and blower resistor connector.
FYI - IMO, ALLData is WAY better than Mitchell.
Steve
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Could be the ground ? If your is like mine, the blower motor mounts to a * fiberglass * box, and has a ground strap from motor body to wiring, or direct ground to engine / body. With blowers turned on, wiggle ground, see if motors start [ sputter than run smooth ]
Usually, power works, or it doesn't. Grounds can get sneaky due to dirt build up, loose screws, excessive paint that flakes off leaving connection loose and corroded. Beefing up grounds on * any * car makes sense !
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Buy er some jewelry.

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