I have an 87 Corvette. I cannot find the fan switch. I jumped the relay switch and the fan came on. First, at what temp should the fan come on, and second, where is the fan switch

The 87 Vette cooling fan is controlled by a switch in the drivers cylinder head located between the front 2 cylinders. The stock switch turns the fans on at 238*. Kits are available (New Switch) to turn the fans on at much lower temps.

I put fans on my 69 Corvette when I added over 100 HP to help cool the engine. I live in warm sunny Southern California that is always hot most of the year. So I bypassed the sensor and run the fans all the time when the ignition is on. It still runs hotter than with the stock engine, but it does not overheat in heavy town traffic. You can connect a hand switch to manually turn it off or on, or run it full time, or as suggested above, put on a kit that will turn the fans on at a lower temp. Remember the newer engines are made to run hotter, and at a factory set temp, run best. Too cool, and the fuel will not ignite properly and you have loss of MPG and HP at the same time. Be careful with your decision. I run a 180 thermostat and the car runs about 180 to 190, but on the highway is is under 180.