I think that people are getting too tied up in how to wire up a winch.
Most people have a winch as an emergency device if they get stuck one day. It is not something they use on a regular basis, if at all.
So how you wire it up is not going to make a huge amount of difference for that couple of times you use it. The different wiring may mean that it takes a little longer to winch out. But what is 5 minutes over the life of the vehicle.
But if you want to get serious about the wiring, these are a few points you may want to consider.
1) Your main source of power is going to be the batteries, not the alternator. So wiring it to the batteries is better than the alternator due to voltage drop across the cables.
2) Voltage will determine how quickly the which turns. The higher the voltage, the quicker you will winch.
3) Batteries cannot produce high amps while maintaining voltage. Just check the voltage at your battery while you are trying to start the car. Typically it will drop to around 8 volts.
4) The less amps you draw from each battery, the higher the voltage and the quicker the winch will turn.
5) So if you can split the amp draw across 2 batteries, you will get a higher voltage to the winch.
6) The AH rating on a battery is typically calculated at what constant amps can be drawn from the battery over a 10 or 20 hr period. So if a battery can supply 5 amps for 20 hours, the manufacturer will typically quote it as being a 100ah battery.
7) The higher the amps you draw from a battery, the less total amps that batter can provide. If regard to Kickarse batteries, their 120AH battery can only supply 264 amps for 10 minutes, or a total of 44 amps. Reduce the draw to 73 amps, it can supply it for 1 hour, or a total of 73 amps. So by splitting your amp draw across two batteries, you will increase the amount of amps available for winching. This could easily be 3 times the winch time for doubling the number of batteries providing the power.
So I would wire the winch to the middle battery. That is, the one connected to the alternator and the one that the second battery is connected to.
Having two batteries running the winch will increase the speed of the winch through increased voltage and will significantly increase the winching time you will have.
The other thing to consider is how much power the alternator is actually providing anyhow. Those that have to winch will tell you that it is usually a wet miserable day when the tracks are slippery. So you are probably covered in mud and cold. So you will have the heater going flat out trying to dry out and stay warm. You probably have tried getting up the hill every way you can before winching, so the motor will be hot by now and the thermo fans are running on and off. It is usually the 5.00pm track that you get caught on, so it is now getting late and you have your lights on to see what you are doing. So how much power is left in the alternator to provide to the winch. The more amps the alternator has to put out, the lower the voltage it will provide to the battery or anywhere else due to the resistance in the cables. The higher the amps the less voltage gets through.
But all this does not mean much if you only winch for a short period once in a blue moon. I just would never wire it to the alternator as it is the lowest source of power when winching.
