'66 Heater/AC wiring questions

[Rust-O-Matic]

I'm trying to sort out the heater wiring in my '66. It has factory a/c, but is missing the compressor. I don't care about that at the moment, just need the heater. Looks like most of the wiring in the glovebox area is still there, but I don't think there's power run to any of it. I replaced all of the other cab and front harnesses with factory type replacements earlier this year, and don't recall where or if there were wires running from the fuse box area or front end to the heater. The original wiring was a terrible mess anyway.

So with that said, I'm sitting here studying the diagram and it looks like there's supposed to be a 10ga. gray wire running from the hot terminal on my horn relay, through a fuse, into the 12ga. orange wire that is currently attached to a relay behind the glove box. I have the orange wire but not the fuse or gray wire. Does anyone know what amperage the fuse is supposed to be? And does anybody have a pic of how this gray wire is supposed to be routed to/through the firewall? I wanna keep it stock looking since the other new harnesses look factory.

Next, there's supposed to be a 24ga. black/white wire coming out of the main harness plug where it passes thru the firewall. That runs to a brown wire, through a fuse, and into the fan control switch. Is this the hot lead into the switch? I'm a little unclear on whether the fan is powered by that wire, or the fat orange wire from the relay mentioned above. And what value should this fuse be?

[jtrichard]

Generally GM AC runs a 25 amp fuse that's what a 67/72 truck runs for heat/ac .... And with a mix of 10GA and 12GA wire that would make sense..

[jtrichard]

The second fuse I believe is in the main fuse block and with AC it is 20 amp and with heater only it is a 10 amp as seen here http://67-72chevytrucks.com/vboard/s...d.php?t=280449

[Rust-O-Matic]

Ah-ha! Thanks fot the info, I totally overlooked the "A.C. & Heater" fuse on the fuse block. The wiring diagram doesn't appear to show it that way so I kinda ignored it. That makes sense though. Any idea why there's two power wires running to the system?

Also still looking for a pic of the wire running from the horn relay if anybody has one. Just curious if it runs along the side of the main front harness or what, and where it goes through the firewall.

[Lokin4AReason]

good to know thread ... for a future reference

[jtrichard]

Originally Posted by Rust-O-Matic

Ah-ha! Any idea why there's two power wires running to the system?

Also still looking for a pic of the wire running from the horn relay if anybody has one. and where it goes through the firewall.

Not enough wire (size) in the main harness to support blower and all of the controls/relays and the compressor so they split the comp off with its own feed (not through the ignition switch also) would my guess

I looked around for pics but did not find any closeups that showed what you need

[jtrichard]

Look here at post #7 http://67-72chevytrucks.com/vboard/s...d.php?t=559436 it shows the power wire coming from the starter bat cable And #9 shows the fuse block and the starter connections

[Rust-O-Matic]

That last link is a fantastic thread! I have spent hours searching and reading about this lately and don't know how I missed that. I just got back to this today, and spent all afternoon trying to figure out what I have, what I'm missing, and how the system works, in hopes of getting the blower motor going.

At this point, I understand how the blower fan switch, resistor, and a/c relay work together, but it's not exactly clear why there appears to be two different configurations for each of the two power wires that supply the system.

First, the 12 ga orange wire to the relay under the glovebox is shown in the diagram on my original post to come from a 10 ga gray wire run from the horn relay. Post #7 in that link about dealer installed A/C shows the orange wire running to the starter. Any idea why they used two different configurations? Were the factory made ones run to the horn relay, and the dealer version only run to the starter? It probably doesn't matter functionally, but I'd like to know what's correct. The openings in my dash appear to be stamped from the factory.

Next is the power wire running to the blower fan speed switch. On the diagram in my original post... what the hell is it trying to illustrate for this wire? Why is the ignition switch shown on the left side, and why does this show nothing at all about the fuse box which contains a terminal for heater/AC? The heater circuit on the fuse block appears to be powered by a red (then pink) wire from the accessory position on the key switch, but the diagram doesn't show any of that. What used to be in my truck was very similar to post #6 in the link above. Just a smaller gauge brown wire from the fuse box to the fan speed switch. This is not what that original diagram appears to show though. Again, could this difference be due to the factory vs dealer installation? If so, please refer back to the first question in this paragraph. Ha!

Sorry this is so wordy. I shoulda took more pics while I was rolling around under the dash today.

[jtrichard]

"Were the factory made ones run to the horn relay, and the dealer version only run to the starter?"..... PROBABLY YES.....The factory ones may have incorporated that 10 gray in the head light harness back to the cal and the dealer ones went to the starter as it would be a cleaner look then running all the way to the horn relay ... Also truck W/O air had 12 from battery to horn relay and MAYBE with air that wire was upped to 10 also? I would guess, so that a dealer did NOT have to change the front harness all the way to the relay and battery that the "KIT" just ran to the starter ...... AS for the schematic in your first post it is NOT a routing lay out it just shows that a wire goes from point "A" to point"B" that is why the ignition switch is on the left also it does NOT show that some of those wires are incorporated in the main cab harness