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I have spent a lot of time working on cowl flap motors. I had a leak in my front engine that it took us a while to find. Under the supervision of my mechanic, I removed my cowl flap motor for cleaning, took it to an A&P radio shop mechanic for disassembly, cleaning, and reassembling, reinstalled and rerigged the motor five times. (I was very glad when we finally got the leak fixed.)
From that experience, I am certain that the light comes on (and the motor stops moving) when the limit switch is actuated. The brushes cannot create the behavior you are describing. If the motor stops moving without a light (and your bulb is good), you have a motor or wiring problem. If it stops moving with a light, you have a switch problem.
I think I fixed about every wiring problem you can have with my motor, because the repeated remove/replace cycles caused me to have to resolder or replace much of the wiring that connects the motor (it kept breaking from too much mechanical movement).
You can test my description yourself, if you can get your fingers to where you need to. You can get someone to move the switch and get the motor moving, then push on the limit switch. The motor will stop and the light will come on, because it thinks the cowl flap is open (or closed, whichever way you are going).
I don't have a wiring diagram any more, but as I recall, the switch was a double throw type, so for the light to go on, the motor circuit had to be broken and simultaneously the light circuit was made. So I don't think cleaning contacts on the switch is going to help.
The fact that the cowl flaps only stick closed (refuse to open) is another clue. Motor brushes would cause a problem approximately equally in both directions. Failing only in the open direction points directly to the limit switch that actuates when the cowl flaps are fully open.
I would replace the switch, and see how things go.
I am not an A&P, this is just advice from a former owner. Please consult with your A&P and decide what you think is best.
Kevin
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