Mods, could we sticky this?
If properly used, no.
I've heard many people (including some mechanics) run off at the mouth about how getting a HO alternator will fry all the wires and destroy your car's electrical system and blow every bulb in your car...
Nothing could be further from the case.
If the proper alternator is selected, installed and operating properly, it will charge up to about 16.0v at the absolute most when cold. Typically after warm up, it will charge everything at 14.4v. On REALLY hot days, it may drop its voltage to 13.8v.
Nothing in your car will be stressed. It is the nature of a generator (alternator) to only supply enough current as is needed, so usually it's just trickle charging the batteries and up keeping the car's electronics.... This is the case for a stock honda 40amp alt or a 350ampre big case custom alternator.
Part of a PROPER install is ensuring the alternator has a sufficient size wire to the battery. If you have more than 150amp alt, I would highly suggest using nothing smaller than 1/0ga to connect the battery and alt.
If you were to use, say, 8ga as a charging wire to the battery when using a 350amp alt, and you suddenly need that 350amps the alt can kick out, you WILL fry that single 8ga wire....
Most alternators come with an internal voltage regulator that keeps the alternator's charging voltage from 13.8-15.5v at all times. Others have external units that allow you to change the voltage the alt charges to.
Voltage is a different beast than current.
Too much current over a small wire will overheat it VERY rapidly and possibly induce failure. However it is VERY difficult to overload a wire with voltage. I'd place a good bet that most of you underhood wires can conduct 500+ volts without much trouble. (Your sparkplug wires carry 10,000volts if I remember correctly, but very LITTLE current...)
The electronics in your car, on the other hand, are sensitive to both current AND voltage. Spikes above 18vdc could very well destroy your car's ECU, bulbs, etc. Current is not an issue as the electronics will only see as much current as they need.
Now to the FOLKLORE/Wive's tales....
I would venture that in the past people saw Racing Alternators and tried to use them in their own cars. Racing units produce a LOT more voltage than normal. (Typically they use 16v.) So most of those alts will charge at 18-21volts DC and that high of a voltage WILL incinerate most of your car's electronics. I believe this is were that folklore began, and is why I said you must select the proper unit for your car.
I've heard the analogies too....
"A HOalt is like a firehose where as your stock alt is a sink facuet. If your faucet had the pressure of a fire hose it would punch a hole in your sink."
Another falsehood, first off the pressure in a firehose and your sink are equal or very close - there is a reason you use schedule 40 PVC or better in your house. The difference is the VOLUME of water being propelled.
Secondarily an alt will only produce enough current as is needed. And if it does go to full power, that current will ONLY go to the electronics that are demanding that much current. So you anticipate where this current is going to go, and beef up those wires. (Big 3 wires, and power wires for your amps.)
This is why a HOalt is COMPLETELY safe for your vehicle.
And I HIGHLY recommend, and use, www.hoalternators.com