Connecting an external fan


Sold, and Replaced
Staff member
May 24, 2001
I want to add a 4" 12v fan, it flows almost 90 cfm, I have my boc (3 10"rockford subs) facing toward the taillights, but the amp is overheating after a period of time. i purchased the fan, and wire, but the fan only has a pos/neg can i use the pos for the remote? this fan has a 3.5 watt, and .32 amp draw, i would rather it go into my power line, but it would always be on, and there is no way i am getting in/out of the trunk every time i want to use y stereo. (BTW the amp is between the box and my rear seat, little breathing without the fan)

amp is a Sony Xplod 760 watt if it makes any difference.
Personally,,what I would do is buy one of those 12v bosch type relays and use the Turn on lead that you are concerned bout to energize the relay,and have the power come from your amp power lead to the relay and thru the relay to the Fan,hope this makes sense..
Or just wait for the PRO's here at give you ideas.
I would get a mechanical or electrical temperature switch and use the relay idea. Only allow the fan to turn on when the ign. switch is on.

High current for the fan should go hotwired through the relay using stereo system power line for the feed. It shouldn't cause noise but if it did you can run a new line or power it off the trunk light power feed.

Only allow the relay trigger to operate with the ign. switch and a high temperature turn on condition.

Hope that made sense LOL.
Make sure that your amp is in an enclosed cabinet with the fan at one end and an opening on the other. I agree with Dennis, I used a Bosch relay and use my turn on lead to activate the relay which turns on my amps and dual cooling fans. I live down here in Texas where 110 degree heat is the norm and my amps stay nice and cool

If your amp is overheating, you could possibly have a low resistance load which will always cause an amp to overheat. BTW, what mode and ohm load do you have on amp?
beats me :D i have a new sony Xplod 760 watt, bridgable, connected to a prebuilt by rockford box containing 3 of their rockford subs with one input, which by the instructions is positive off of one and negative off another, i do like the loud bass, and the amp has very little room to breath so i am attibuting that to the issue, when my box is turned around i am not experiencing that, (or didnt)

If you have a DVM, set the scale to ohms and measure the positive and negative lead of the speaker inputs of box. If your amp is stable at 4 ohm mono and you have a speaker impedence reading of 2 or less, you will have overheating problems. The speaker reading should be reading apx 3.7 to 4.1 and that is a normal reading for a 4 ohm load. If your amp is stable at 4 ohm mono and you have a 4 ohm load on it, you shouldnt have any problems unless you are driving the hell out of the amp and that can lead to an overheating problem. An amp rack with cooling fans will help out tremendously. Let me know what your specs are and the reading of your speaker load.
Frequency Response -- 5-50,000Hz (+0/-3dB)
Harmonic Distortion -- 0.005% or less at 1kHz, 4 ohms
Speaker Impedance -- 2 - 8 ohms stereo, 4 - 8 ohms bridged
Input level adjustment range -- 0.2 - 6.0 Volts (line level), 0.4 - 12.0 Volts (speaker level)
Power Supply Voltage -- 10.5 - 16 Volts
Current Drain -- At rated output: 40 Amps at 4 ohms, remote input 2 mA

from the sony homepage, and rockfords are

4 ohm
200 watts rms
400 watts peak

am i overdriving the amp? if so, will the fan help?
One way could be if the amp gains are over tweaked and or having the volume up all the time. I doubt if you are over driving it. Amps especially bass amps get extremely hot, so hot that you cant touch the heat sinks and thats ok when you have ample cool i.e. ventalation, cooling fans. If the amp overheats, does it go into protection? or does it get very hot?. My RF Power 1000 got so hot that it burned a blister on my arm while I was tweaking another amp. If the amp is getting hot and doesnt shut down, I wouldnt worry about it, but I would consider an amp rack with a cooling fan or 2. You would be suprised at what a difference it makes.
The specs you gave me on your components are fine, at least you are not at a 2 ohm or less load, then you would have problems. Let me know what all your amp is doing as far as shutting down or not.
i purchased an auto relay @ radio shack today (with the specs on my 4" box fan it shouldnt matter about the relay much) and yes the amp shuts down, if i put the volume up, i will probably lower the gains a touch after installing the relay on the back of the box is the wiring diagram for it, i will be putting that in tomorrow night.

thanks for the help your giving me, and as for an amp rack, i just have 2 amps screwed to a factory rockford box (got an awsome deal on it) so i can take it all out at once for racing.

I really like the system as except for the amount of vibration you hear behind the car you really have no clue how bass'y it is inside :)