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Got a 71 w/ a/c and gauges and trying to staiten out wiring some moron fixed, anyway
got a wiring dia from ausley's(osborne)dos'nt
show any A/C or gauge wiring. I have a heavy
(approx 12 ga.) orange wire from smaller block behind booster that was tapped into the purple start wire, I know it dos'nt go there, anybody know ?. Also have a relay
#3990842 hanging from evap. case 1 double conn. w/tan and blk(thats been cut off) and
1 single w/ light green, any ideas what this is for, Thay actually had rigged a toggle switch under dash to supply power to A/C compressor. Any help greatfull or where can I get a diagram for a 71 w/ air.
Thanks, Rob...
 

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A/C comes with its own harness under the dash, so expect some extra wires under there. The orange wire (always hot) goes into the heater motor relay, from that a blak/purple wire (don't remember which right now) goes to the blower motor. There is a pair of TCS relays behind the distributor, if one of those is the one you're talking about, they're pretty useless and can be removed. The heater relay is on the heater box, if this is the one, then you'll need a real diagram.

I got the diagram from somewhere (Gold Eagle, I think) but it is not complete. There are several (three?) distinct diagrams for various setups, and the A/C stuff is not there wirth a darn. Get yourself the full assembly manual; it's all there.

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Cecil Hawkins
San Diego, CA
1971 GMC Sprint

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Cecil is right about the manual. Easiest way to find the information.
The orange wire sounds like the wire for a non-A/C set-up. It is not used on your car. Not sure why someone tied it to the purple start wire. Maybe a theft cut-off idea?
I don't see a tan and black in that area. Tan and dark green plug into the blower resistors.
Sounds like the guy had a problem with the heat/A/C circuit and had a field day rewiring. Problem is/was probably in one of 2 places.
1, The lever switches that operate the temperature.
2, The blocking relays which may be under the dash, right hand side, near the inside heater box.
 
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