I put new wafer thermostats and micro-switches in the ole #416 incubator. Spent 2 nights trying to calibrate and get it set up right. Nothing would work. I'd get one set and then the other would not work at all. I'd back off on the working one and try to set the other and then it wouldn't work either. Serious frustration going on there. Last night, I was minutes away from ordering electronic controls to put in it. I really didn't want to do that, I tend to be a purist about antiques.
So I says to my self, "Self, check the wiring. If the T-stats and switches are new, the only other thing is the wiring." Turns out that a previous owner had wired the 2 thermostats in parallel instead of in series. They were fighting against each other.
Fixed the wiring this morning and started it running. Set the temps and let it run. Was holding good until I left at lunch time. Hopefully it's still on track when I get home this evening.