[wraprail]

A relay is a switch that can handle loads with high current draw such a a cooling fan. Then you can use just about any switch you want to switch the relay. One advantage of a relay is you can mount the relay close to the battery and the fan with very short wire runs. Use large guage cable (# 12 min. 10 better) from battery, to an inline fuse to relay then to fan+. Run fan- to a good ground close to fan. (Frame or crossmember. Make sure you have clean bare metal). Now you can run small guage wire from the relay to whatever switch you want. You can use positive or negative to switch the relay. The best switch to use is a temperature switch screwed into the water jacket that turns the fan on and off automatically. You can get one on ebay for less that $20. Then you can add a switch over ride for manual fan control. Thats what I do. Relays are cool. Once you understand how they work and what they can do you find all kinds of uses for them.
Just think of a relay as a remote switch that you switch with a switch.
Oh yeah, as stated above if you just use a switch and no relay you will either burn up the switch or the wire running to it or your fuse box will melt. When you have long runs of wire you have voltage drop. By the time you go from the battery to a switch inside the cab and back to the fan you would be like 9 or 10 volts at your fan. If the wire or switch somehow didnt fry your fan will get hot and burn up cuz of the low voltage. With a relay you have short wire runs and almost no voltage drop.
Ok thats enough.
Later.
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