Questions about installing an electric fan

[WH23G3G]

Is it possible to install an electric fan without hacking a new wiring harness? We have universal electric fans where I work depending on what size I want. I just don't want to hack into my new engine harness. How would it be controlled? Can you flip a switch to turn it on when you see the temp going up? What is the appropriate size for a 400-4BBL, all new A/C components, not charged yet until motor is broken in? Maybe once I've got the engine tuned right I won't need but can you still install it and have it there to help cooling? What all does it take to install? Should I have a shop do it? 

[ChargerST]

Yeah, pretty easy to do actually as you can build it around your existing harness. Then fan only needs 12V (from alternator side - you can use the alt output stud) and ground. To switch it on use a relay in either the ground or 12V wire (I prefer 12V to be switched). The relay has to be grounded as well - just find a good ground spot for the fan and the relay. Then just run a wire from the relay to a switch inside the cab an from there to a switched 12V source (you can use a free spot in the fuse box). No cut wires anywhere.

there are more sophisticated layouts but almost everyone can be done without hacking into the harness. I would add a thermoswitch that turns on the fan - you can still use the cabin switch to override the thermoswitch.

[ChgrSteve67]

There are fan controllers available.
Generally they just need 1 wire for ignition power so the unit turns on and off with the car.
Another power source to run the fans that comes directly from the battery with a inline fuse.
Chassis Ground.

Optional wires are
AC power feed so the unit will turn the fans on when you turn on your AC
Fan over ride switch that will either be a power feed or ground depending on the unit.

One of the units I use to use had a temp sensor that was connected to the control box and the sensor was installed in the fins of the radiator.
http://www.summitracing.com/parts/FLX-31149/

Here is another unit from painless. Looks to be more complete but also more expensive.
http://www.summitracing.com/parts/PRF-30141/

The system I use today is from BeCool and actually has a temp sender located in the water pump housing.

I'm currently in the process of adding a secondary fuse block under the hood for all of the accessories and fans currently connected up the pos batt term. After its all cleaned up I plan on taking pictures of everything and posting them in a thread.

[Nacho-RT74]

Another power source to run the fans that comes directly from the battery with a inline fuse.

with amm in the system thats wrong