Originally Posted by RavensOracle
. . . . I like to use color coded wires - red is hot, black is ground . . . .
Except when you get into trailer and 'Stick-n-Staples' RV wiring, where black is hot and white is ground like AC wiring - be careful when mixing and matching equipment.
If you only have one battery string, using the vehicle chassis as your ground should not make any difference. If you have multiple strings, say four 6-volt house batteries in 2+2 configuration, it may make sense to use a bus bar to keep the battery wiring resistances nearly equal in order to balance the charge and discharge rates between the pairs. Plus, if you use battery capacity metering like a Tri-Metric, you will need to have a special large capacity/minute ohms resistor between the battery minus and ground in order to develop the signal to the meter. Having a battery ground bar insulated from the chassis is one way to have a place to connect the metering resistor.
The difference between solid and stranded wire has been debated here before. There is no specific conclusion, only what each person feels is most comfortable with for their bus. There is, as always, a cost versus quality decision to be made.
A number of RV manufacturers use solid house-type wiring in their AC wiring, and have the RVIA/NFPA specs written to accept it. In general, solid wire is to be used in places where the wire is bent once for installation, and does not move again after that. Solid wire that is bent back and forth will eventually break, just like snapping a piece of coat hanger. Some skoolies worry about road vibrations, and will not use it.
Wire that is meant to be bent, like extension cords, is instead made up of many strands of smaller conductors bundled together. Some stranded wire has a few thick strands, other wire has many, many fine strands. The smaller the strands that make up the bundle, the more the wire can be bent back and forth without harm. Wires for permanent fixtures probably don't matter, wires for accessories that move around like laptops or table lamps should definitely have stranded wire. The same is true for battery or generator wiring if there is a slide-out tray that requires the wires to move.
A word about stranded wire - if you see bare copper-colored strands inside the insulation, the wire will not be moisture resistant. I have seen my share of wires where any compromise of the plastic jacket that lets in moisture, even smaller than a pin-hole, lets the moisture turn the soft copper wire into hard, green powder. This powder will show voltage OK on a sensitive meter, but will not allow enough current through to run anything at the other end. I am not talking about "cord," where several wires are run together inside another protective jacket, but single-conductor colored 'hook-up' wire purchased from the auto parts or Radio Shack store. If the wire is "tinned," showing silver-colored conductors where the copper was bathed in solder before being put into the insulation, the wire will be more moisture resistant and last longer. It will also be easier to make solder connections to, as the solder has already been flowed into the molecules of metal in the wiring. (Solder is not "glue," but is a metal-to-metal bond.)
Good connections are much more important at low voltages than at household AC levels. A 21-watt turn signal bulb used for lighting draws 1.75 amps at 12 volts. A 25-watt incandescent AC bulb only draws 0.2 amps at 125 volts. A two-ohm resistance from a bad wiring connection would create 2.7 watts of heat and dim the DC bulb by about 25%, but at AC the heat would only be 0.4 watts and there would be no noticeable affect on the brightness. The same 2 ohms on a 12-volt, 600-amp starter cable would create 72 watts of heat, and limit the starter to 6 amps. If the connection were only half an ohm, it would supply 24 amps to the starter, generate 288 watts of heat, and give the impression of a dead battery until the fire started.
Some Skoolies will spend extra money and only use marine-grade wiring on their buses, with smaller strands and presumably higher quality insulation. They feel the extra money buys peace of mind. This may be a little bit of overkill for most of our purposes. But paying attention to what kind of wire we use, plus using zip ties, tubing, or other supports to prevent unwanted motion of the wires will go a long way toward making safe and reliable wiring.