Old timer told me to never trust the wiring diagram, he was dead right

I was doing a panel swap at a house built in 82 last week, and the diagram showed the door sensor on zone 3. But the old wires were a mess, yellow and green mixed up everywhere. If I hadn't listened to that retired electrician who told me to always tone out every single wire first, I would have had a false alarm on day one. Has anyone else run into a house where the original installer just made up their own color code?

2 comments

2 Comments

the_richard22d ago

82 house, yeah that tracks. I had a 1983 ranch where the previous guy used leftover computer ribbon cable for the thermostat wire. The diagram showed green as common but it was actually the second stage heat. I spent a whole afternoon chasing a ghost because I took the print at face value. The original installer probably just grabbed whatever spool was closest to the truck that day. You learn real quick that wiring diagrams are just suggestions, especially once you hit the 70s and 80s. Some guys treated those installs like a personal art project.

nina_harris21d ago

Tone out every wire and forget the diagram exists. That ribbon cable thermostat story is brutal though, I feel that one. Had a 78 house where the guy used thermostat wire for door contacts and vice versa, just swapped the colors around for fun. The original print showed a totally different color code than what was actually in the wall. Diagrams from that era are more like a rough guess than a real map.