Brian,
You are correct that a GP that increased its resistance would draw less current and would not get as hot.
However, I have never seen a GP that changed much in resistance before they burned out completely. And remember you are measuring cold resistance which is not always a good indicator of the hot resistance which can only be measured by measuring the hot current and the voltage applied.
The best GP test is to connect them directly to a good 12v car battery and observe how hot they get. If they don't glow a bright orange, they should probably be replaced. I would do the visual hot test on any GP that measured over 1 ohm cold.
P E H
|