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Discussion Starter #1
The schematic on the info site at https://www.alfamontreal.info/Montreal/ColourSchemaAC.pdf incorrectly documents the wiring around the blower switch and indicator light. It shows the indicator light being driven by a red/black wire from the A/C temperature control #74 (the one on the left of the HVAC panel on the dash). In fact, the indicator is driven by a yellow/black wire coming from the 4-position blower switch #72 (the one on the right side of the HVAC panel). This makes more sense since the red/black wire really only turns the compressor on and off. The voltage on the yellow black wire exists at four levels, 0 VDC plus three higher up to about 9 VDC, depending on the position of the blower switch. This gives the blower indicator light the interesting property of not only indicating when the blower is on, but also potentially what level of blower speed is in use, just in case you need to know that.
 

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Be leery of all Montreal wiring schematics.

On my 71 (I think) I ended up using three different schematics during the restoration. My harness contained everything to operate AC, but the car had none of the hardware for AC. Probably saved money to build one type harness for differing configurations, but even there I expect mods were made from year to year as well. I also had some elements for RHD.
 

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That’s kind of my point. What is incorrect? If several cars have different wiring schemes then there cannot be a single “correct” schematic.
 

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Discussion Starter #5
“Incorrect” is when the drawing you have does not reflect how your unmodified car was built. If in fact there are factory variations we need to know about them. The only way we will know about them is if everyone reports in.
 

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I presented my findings in the BB blog of my Montreal restoration.

My conclusion was it was a poor use of time to expect a perfect consistency from car to car with low production Alfas. I’ve encountered similar, but less complicated variations in the old 102-series, of which something around 3,414 were built.

As I noted above, I ended up using three different published wiring schematics, each differing from the others, to work through my wiring connections.

The fact that at least three different schematics were published tells us Alfa introduced changes at various points. Meanwhile, none of the three schematics I found commented upon a wiring harness having connections for both LHD and RHD cars. I also don’t recall the schematics noting changes by serial number or year.

Among other things, my car did not have a hazard light switch, nor a hole in the apparently original center console to hold one. I bought a new production console which came with a hole for that switch, so I bought a switch and installed it, hooking it up to the already-present wiring harness. I recall needing to search for a schematic showing the hazard switch details. My car was relatively early, but we have evidence of future changes being planned, but not necessarily documented in the contemporary schematics.

So, good luck seeking consistency, or even accuracy, in low-production Alfas.
 

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Discussion Starter #7
You’re putting a lot of words in my mouth, Don. I’m not seeking “perfect consistency” and I never said anything like that. I’m also frustrated by missing or inconsistent documentation and I’ve experienced much worse than the Montreal. Try restoring a car with no wiring diagram whatsoever. You don’t need to shoot the messenger just because I may be more optimistic than you about crowd sourcing of wiring deviations. I have a lifelong history with electrical engineering and documentation thereof and I’m not intimidated by the complexity represented by the Montreal. It’s utterly trivial compared to what I’m used to.

So we can throw up our hands, or we can try to improve the situation. Courtesy of Gene Brown we have wiriing diagrams that are likely correct to the very high 90s%. If we treat this forum as a repository of technical information and consistently report any found errors into a common place (a ”sticky” on this would be nice) it will at least help other users in navigating the variations. All it takes is reports like mine, and after some accumulation we would likely get really close to 100% coverage.

So regarding your “blog” what search terms would I use to find the wiring diagram errors you encountered?
 

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Discussion Starter #8
Additional information, on my car (as opposed to the schematic) the wire illuminating the "Vent" light is gray black. The wiring diagram shows no gray-black wire between there and the blower switch, so the colors on the diagram around that switch are likely wrong.
 
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