[torbjorn]

Yes, the original fan probably has a built-in hall sensor to sense its rotation. Fans with such sensors are common as CPU cooler fans on pc motherboards today, as most motherboards require the sensor signal for supervision.
It should not be a big problem to find a suitable fan at a computer store or just robbing it out of a scrapped pc.

[swmcoach]

I have a Panasonic LCD projector built in 2003, sorry do not have model number right now. Anyway it would power up from standby for about 30 seconds then shut down. I noticed the fan that cools the projection bulb was not working so I found what I thought was a good replacement. The only thing is the old fan has 3 wires, black, brown, gray, while the new fan has just 2 wires, red & black. I connected the brown from original to red wire of new fan & black to black while not connecting the gray at all. Now the fan comes on but the projector still shuts down after about 30 seconds after powering up. Is the gray wire possibely causing this? Is it some kind of sense wire? Please help.