i get home from cruising around and i notice some smoke trickling out behind dash trim. i yanked that bitch up and the female spades going to switch are melted. the wire was hot too. the switch is fed power via 14 ga wire then goes back to fans. do i need to run 12ga wire or should i just tap the damn thing off the fuel pump fuse and not worry about switch. i have a 30 amp fuse inline i would have thought that would have blown. idk

 

I'd take a look at your fan, I think there is something wrong with it. Most fans don't draw more than 10 amps usually, so you've got problems. You should be using a relay on that fan though, and just using the switch to trigger the relay. A fan is an inductive load, and a relay has bigger contacts and is much more suited to switching that type of load than a dash mount switch is.
Check the fan, check the grounds, check everything.. I'm guessing the switch and the spade terminals are causing too much resistance through it, which dissipates power as heat. That is probably using the wire as a heatsink, which is why the wire is hot. There could be corrosion somewhere too..

There should be no reason you need a 12 gauge wire for fans, 12 gauge is rated for 40-50 amps for lengths less than 10 feet. 14 ga is rated 30-40, so you shouldn't need anything that big either. I use 18 ga for our racecar, and that's overkill. Our fan draws 6 amps..

 

Installing the correct relay will solve your problem.

 

find the voltage drop, or put the relay on the ground side. you can run a micro relay if you do that, since there will be not much current, only a small voltage drop. same reason you can run a microswitch on the ground side of a circuit, but if you put it before the load that fucker will melt in a heartbeat.


i have an 18" pusher fan that draws 7.4 amps at full tilt, you have a problem.

 

i put a 30 amp fuse inline, because thats what i read somewhere. i put a 10 amp fuse inline and its fine. someone on another site recommended a relay too. thats what i will do tonite. there is nothing wrong with fans, they are brand new. i checked ground that is good too. the load def must be to much for the switch. thanks guys for the help. relay ftw

 

Not to say you're wrong, but...you're wrong. It doesn't matter where (before or after) a load the switch or relay is, you're getting the same current through it. It's physics, and you can't dispute those laws. Current is the same everywhere around a closed loop, which in this case is from the positive battery terminal to the negative battery terminal (with the fan in the middle). The energy used to power the fan is the electrical potential energy (which equates to a voltage) that moves a current through the fan. Current is just a charge with some energy behind it, and you can't create or destroy charge, but you can use the energy that moves the charge around. That is what powers the fan. If you want to prove me right, run the wires through a multimeter before the fan and after the fan. The current will be exactly the same (or else your multimeter has some accuracy problems)..

 

The 30 amp fuse is for startup overhead, if you have a 7-10 amp fan, it will draw a large spike of current on startup (that's what inductive loads do) so if you have a lower amp rated fuse, it will blow.

 

so the 30 amp fuse is fine then? i dont want overkill. would i even need the fuse if i run the relay? i have some 30a spdt relays in my shop i can use. lmk

 

You still need the fuse, yes, it's protecting the fan and the wiring. 30A is a little overkill, twice the rated current of the fan should be fine. The fuse still has the same job when you're using a relay, it's just inline with the relay now instead of inline with the switch. Put the fuse as close to the battery as possible. You're really protecting the wire and/or fan from catching on fire in case of a short circuit, so the less wire you have before the fuse, the better protected you are.

 

the fuse is right at my distribution block in engine bay. ill check the rated current on the fans tonite and determine what fuse i need. thanks Fabrik8