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http://www.feathersite.com/Poultry/BRKIncubation.html
One of the things that I found is, that sometimes you have to adapt your plans to the materials that are available. At 1st, I was gonna use A-C exterior plywood to make a plywood incubator. That idea flew out the window, as most of the lumber yards or Home Improvement stores in my area don't carry that type of plywood. I was worried about chemical leach, etc., from plywood that wasn't particulary friendly towards environments where most eggs grow, a moist humid environment.
Another thing not readily available to a DIY incubator maker (at least locally) was a decent, low watt heating element. At least I didn't know where to find one.
What I did end up using was a 70 quart Coleman cooler that was modified. I used 2 porcelain lightbulb sockets. I also recycled 2 fans from an old computer that no longer works. I bought a thermostat online. There's the guts. I also had some copper wire already sitting around that I was gonna use to make stop motion animation armatures with. Think it was 16 gauge.
Keep in mind that things should be wired up by people experienced with electricity. Or else it's at your own risk. Things like electric shock, and wire apt to burn under certain circumstances. It's always a good idea to unplug it before modifications are made. Just standard cautionary practices
For the wiring, I wired the 2 lightbulb sockets in parallel. It's more of a backup, in case 1 fails. It's also a secondary heat source. The thermostat goes inline with the light sockets. I also used a 12 volt transformer for the fans. Just a few thoughts. Good luck on whatever you decide to do.