thanks brent keep me posted. trying on my end no luck yet joe

 

I didn't read all the posts, but on my 77 (now sold) the AC harness plugged in to the heater harness and anded up sort of as a piggybacked system. After it was plugged in, it ran over to the AC system from there. The clutch wire was run along the liquid line/suction line pair from the firewall side, everything else was inside the cab. I converted my 77 from heater only to factory AC. The biggest issue I had was to cut the enormous hole through the firewall. I think you may be able to use the harness from any 73-79 F series pickup or Bronco.

 

Nope, they are different.

1973-1974
1975-1977
1978-1979

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It all has to do with how the Orange Wire is wired to the fuse panel and ignition switch to the battery.

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1973-1974's has one Circut #37 Black/Yellow wire that has a Direct link to the Battery. This One wire can supply power to the Following circuts.
#33 Yellow: Horn Relay
#21 Yellow: Ignition Switch
#526 Black/White: Roof Marker Lamp Switch
#25 Black/Orange: Headlamp Switch
#363 Red/White Turn Signal Switch
#181 Orange Heater Blower, or A/C Mode Switch
#297 Black/Green: Radio, Wipers washer.

Etc... On trucks without a/c, this wiring was fine, but however with trucks with A/C And with all these working at the same time, it caused an overload of the #37 Black/Yellow wire so in...
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1975-1977: They used an accessory safety relay, for a direct feed from the battery could be used to operate the A/C heater blower motor. Thus eliminating the overload problem on the other circuts. This Accessory safety relay, is wired into the A/C-heater Harness.

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In 1978-1979, Circut #181 Orange has a Direct Link to the Battery through the Ignition Switch to the fuse panel, to the Heater blower. This eliminated the need of the accessory safety Relay, therefore the A/C Heater harness on a 1978-1979 will not have the provisions for the relay.

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Hope this makes sence.

 

Excellent! :)

 

hey guys my name is joe from new jersey. Im still looking for a wire harness and a safety relay for my ford for fac ac. Im following 81-f-150-explorers advice, looking for this harness if anyone has one let me know or parting a 1977 ford with factory ac let me know thanks (joe from n.j.)