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Cooling Fan Override Switch

Thanks to Mac

* The author (and V8SHO) makes no claims or guarantees that this modification will work properly for any vehicle. If you choose to modify your vehicle based on these instructions, you do so at your own risk. Installation of this modification could damage your vehicle or void your warranty. Since I don't have a warranty, I don't particularly care.


1. Switch (SPST)
2. 18 gauge wire (approx 10 ft)
3. 1ea terminal connector
4. 1ea wire splice
5. 2ea female blade connectors
6. Optional fuse holder and .3 amp fuse
7. Electrical tape

This modification installs a switch that grounds the # 46 (LG/P) wire on the PCM connector. This will allow you to actuate the relays for the high speed side of the cooling fans thus turning you fans on to cool you car at you leisure. This does not affect the normal operation of the cooling fans.

Step 1

Step 2


Step 3

Step 4


Step 5

This is normal)

My A/C didnít work at first but after I shut car off an restarted it the, and turned the A/C on and it started working again, it has ever since. I have read where this has occurred before while install I performance chips. Educated guess is the computer is re-learning all it things due to pro-long power outage.

Good luck and enjoy you new Mod.

Comments & Observations Section

eh? cooling fan over-ride switch? What's the point? Wouldn't you WANT a cooling fan on? Or does this mean you can turn it on and off at will?

Ryan S.
97 TR
Porterized w/ K&N panel
Dynomax Thrush Turbo Mufflers

This looks very good. One question is if you forget to play with this switch and leave it in the off position will this cause the fans not to work and over heat the car?

I have done something similar on a Chevy years ago and forgot to flip the switch and overheated the car.

Kirk J Doucette
Commander of the White Lightning Assembly
97 White V8

You might want to be careful running it this cool on the street. With older Mustangs the computer thinks the engine hasn't warmed up and it runs too rich, possibly killing the cats and possible other damage. Maybe the newer computers are more sophisticated than this, I don't know. Keeping the intake charge cool is what generates power. I think either whrenchhead or jegs has a 170F thermostat for the V8.

Paul Nimz
'97 Tr
'93 mtx

Caution is advised in doing this mod. Remember the cooling system is backwards, similar to the late model Corvettes. Mustang mods in general will not yield meaningful performance changes in this car, all the ideas for better performance come from this list, although new ideas are welcome, we don't want to see you lunch a motor and major $$$ without a spirited debate about this here. This is a special motor.

'98 TR

Okay all this mod does is allow you to turn on your fans when you want them on. Like on the drag track. A cooler motor (proven in time slips) at the track produce more power (ie cold mornings). The thing is the mod will only cool the car to factory thermostat temp. This should not hurt anything considering the cats are already warm. The computers is the same type EEC-V on 99 GT that is in the SHO (only the programs are different to accommodate the car/engine type). I am not a mechanic but this does work and I havenít hurt an motor yet. I only use this at the track to keep the car cooler anyway. I hope this help make this mod a little easier to understand .I am for cross talk I always learning..... Thanks


Yes you can turn fans on high at will. They will work with ignition on engine off or a with engine on ..... end result car will run cooler for racing. Next I am working on is an cooler thermostat to go with this mod anybody have ideas?
This mod allows you to turn on the fans before factory preset. allowing you to cool car faster with engine off (Ignition on) or at idle. Bear in mind this will only cool the car to the thermostat temp (195 deg). I am not sure on the stock thermostat. I hope this explains it better. Cool motor tend to produce slightly more power.

Do you have it set up so that the fans will run with the engine off?

Paul Nimz
'97 TR


Yes but,

you need to leave the ignition on with engine off or a with engine on .....(that is the only downside I have had) You need to have power on.


What are you using for a signal?  What is wired to your switch?

Paul Nimz
'97 TR
'93 mtx

To all who replied,

Cooling is reverse flow on the 99 GT and Cobra same as LT1 and LS1 and the same as the V8 SHO....... go easy on me I can take anymore..... :) No seriously I research allot before I attempt anything no matter what I car I modify.

Thanks for the Reply's....


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