This is one that should be common sense, but i have seen vehicles where the owners overlook this. Whenever you upgrade the alternator output to a vehicle, or change to higher amperage batteries, or even set up dual batteries, always watch where the wires are run very closely.
When i wire everything up, i used heavy gauge wire, with insulated clamps to mount the wires to the inner fenders, away from anything that would cause an issue with it, and run the wires for the dual batteries through the firewall to the switch in a short piece of conduit bonded to the firewall.
If you wire through a hole drilled in the firewall, with no additional insulation of any kind, the wire's insulation can rub through and cause it to catch the vehicle on fire. This can be easily prevented by using a readily available rubber grommet to insulate that one wire where it goes inside the cab.
I have worked on many vehicles in the past where people don't pay attention to things that could cause an issue later on down the road. Safety should always be first and foremost in any vehicle repair or upgrade of any kind.
On my 1994 Dakota, i have switched dual batteries, with the switch inside the cab, for ease of access, a higher output alternator, 1200 watt two channel amp, electric over hydraulic Meyers plow, 4 combination driving/fog lights on the front, hard wired 1800 watt power inverter in the cab, and all of the wires under the hood are run through PVC conduit that is attached to the truck with insulated hard rubber/metal clamps. The wiring in the cab is run through double layer flexible plastic, like the manufacturers use, that way i never have to worry about a fire, or a wire shorting out at the wrong time. I know running conduit isn't always practical in some vehicles, but even flexible tubing, and rubber grommets, are better than exposed wiring everywhere.
And, no matter what you are wiring, from aftermarket lights, to stereo systems, to winches, plows, whatever it may be, zip ties are a very inexpensive and valuable addition to any toolbox.