Have to jump in here... (long time lurker first time poster)

I don't think that's an 820 ohm resistor, its 520 ohm. Bands are read left to right with these older resistors the banding is grouped to one side. You never start with a metallic band

rockon

; the metallic is the tolerance band and is always on the right. So the green is 5, red is 2, the brown is the multiplier so x10, with the silver being the tolerance of ±10% for the total resistance of 520 that could read as little as 515 to as much as 525 ohms.

I suspect this is part of a voltage divider circuit... the gauge likely can't take the full 12 volts or it would peg the needle. Instead the temp probe, which is a variable resistor, is wired to this known fixed resistor in a voltage divider circuit to drop the voltage to an expected amount. I dont know what the rating of the probe is and couldn't find an electrical schematic after a few drinks tonight but for giggles let's say both resistors were supposed to be 520 ohms, this circuit would drop the 12 volts in down to 6 volts out. If one of these 50 year old resistors started to fail and increased to 850 ohms then that 5 volts is now 7.445 volts. If the gauge was expecting one thing at 6 volts but now was getting 25% more juice then things could read incorrectly.

Everything in that temperature circuit should have a known value to it found in a schematic somewhere. Just needs to be checked off one by one. It would be dumb but cool to buy a fancy new shiny when a 5 cent part would have fixed it.

Love your videos dude, keep it up and have fun at OSH. Told my wife about your bit about shoving the money in to fix the problems and it was the first time she didn't say 'and that's why we dont own a plane' so I'm thinking there's a chance...

Cheers - Brian