From MP3Car.com Wiki

MP3Car Car Computer Installation Standards

The MP3Car.com installation standards have been formulated to promote system durability and longevity.

The marine and auotmotive environment is a harsh one for computer equipment; heat, vibration, chemical compounds and other factors are constantly at work undermining the efforts of the most conscientious installer.

Factors that will affect the durability and longevity of the computer system need to be taken into account when designing an installation procedure in order to lengthen longevity of the system.

Batteries Secured

Batteries connected to any charging system, installed anywhere in the vehicle, should be secured to the vehicle in a manner which will not allow for movement in any direction with a reasonable amount of force.

Power Wires

Appropriate Power Wire Size

Proper sized wire gauge should be used for both positive and negative current requirements.

The below chart shows the minimum copper wire size acceptable for normal wire lengths used in a vehicle to meet normal current demands. If aluminum wire or tinned wire s used, the wire gauge size should be even larger to compensate. The wire size calculations are intended to allow no less than .5 voltage drop to a circuit, assuming the wire is properly terminated.

Appropriate Power Wires Fused

All electronics throughout the computer system installation must be individually fused (a fuse that is in line with each (one) piece of electronic gear) with appropriate value fuses. Chassis-mounted fuses on electronic equipment satisfy this requirement. Items mounted inside the computer case do not apply to this standard.

 NOTE: All system power wires connected to any positive battery post must be fused within 18 inches of wire
 length from the battery post and prior to the power cable's first pass through any sheet metal or other
 conductive material. 

If there is no fuse present or the fusing is located beyond 18 inches or 46 centimeters of wire length or after the power wire passes through sheet metal, warranty will be voided. Alternator wires do not need to be fused.

 NOTE: Banks of batteries located within 18 inches of wire length between each other may be evaluated as one
 battery and the wire between them need not be fused. Factory dual battery systems (usually found on larger 
 diesel-powered vehicles) often do not have factory-installed protection between batteries. - Additional protection 
 is not required in these cases, unless the cable and/or battery/ies have been upgraded.

The purpose of fusing is not to protect the component, but to protect the wire. The wire has to pass through and by a multitude of sharp objects. The potential danger here is that these sharp areas can cut into the plastic cover on the wire and cause a short to ground.

All fuses shall be installed in a weatherproof, rubber-type holder or a circuit breaker of proper amperage.

The correct fuse or breaker must exceed total amp draw, and be able to handle the total amperage. Self-resetting circuit breakers are not adequate. These types of circuit breakers are undesirable due to the fact that they can reset themselves until the contacts permanently fuse.

The chart below demonstrates the proper fuse size to be used to be within warranty limits.

These are the recommended maximum fuse ratings for the corresponding wire size. Using a smaller fuse than what’s recommended here will be perfectly safe.

Wiring

All Wires Properly Protected

The grommet and sleeve must provide protection against elements common to the area in which it is installed.

Examples: Under a vehicle the grommet/sleeve must be water tight and protect against common road debris (salt/sand/dirt/water/rocks etc). In an engine compartment the grommet/sleeve must be able to protect the wiring against common engine compartment conditions (such as spilled engine fluids, water, dirt, heat, etc). Never run wiring through holes that have rough metal edges.

 NOTE: A non-conductive grommet must protect all wires where they pass through any metal panel or 
 against any metal edges. Additionally, a non-conductive protective sleeve (a wire’s insulator is not 
 considered as a protective sleeve) must protect all wires that pass along, by or against any potential 
 hazardous metal. This includes, but is not limited to; all power wires and speaker wires.

All Wires Properly Terminated

Terminating the end of a wire should be done as carefully as possible.

All connections of wires at terminations and both positive and negative terminals must be protected from potential shorting and/or corrosion. All wire conductors (copper, etc.) must be insulated and not exposed at all.

When using a crimp-tool, the seam of the metal barrel, unless it is seamless, should be in the concave part of the crimper’s jaws. This makes for a secure mechanical connection.

For connections in the engine compartment of a vehicle, it’s important to solder the connection and then heat-shrink the connection and terminal with a piece of heat-shrink tubing. The tubing must cover the bottom of the connection (where the wire enters the connector), as well as go all the way to the top of the connector. Cover as much of the connector as possible making a good weather resistant seal.

Non-corrosive grease shall be applied to the ground as it attaches to the vehicle. This help to reduce possible corrosion of the screw head and the terminal.

Solder should be applied so that it flows over the connection. A good solder joint should be smooth, shiny, and concave.

 WARNING! No wire nuts shall be used in the install.  Wire nuts were designed for a stationary, stable environment
  – like inside a house.  The wire nut will eventually fall off the wire leaving the exposed wiring to short to ground 
 or to a component.

The following examples satisfy this section requirements:

Terminals:

• Terminals that are coated or plated

• A complete or partially sealed enclosure surrounding the terminal (battery venting or “vents” that allow gases to escape from the enclosure are acceptable).

• A non-conductive water proof grease covering the termination
  

Wire Termination:

• A heat shrinkable material that provides no means of fluid penetration

• A non-conductive water proof grease covering the exposed wire (example at the terminal connection end of a crimp connector)

• Terminating wiring should always be soldered, and then heat shrink tubing should be applied to cover the complete joint. The high vibration environment should always be taken into consideration when wiring.
  

 Note: Waterproof grease should be used to stop corrosion penetrating up the cable.

Wires Secured

All wires should be neatly tied at regular intervals (maximum 12 inches apart) and routed in a neat and orderly fashion so as to prevent them from interfering with the mechanics of the location in which they are installed. Any type of tape or glue is an unacceptable means of securing wires in any area that is exposed to the elements.

Grounding

The ground is a place with a good physical connection to the same metal that the vehicle battery ground itself shares. Make sure that it has the same ground potential as the battery ground; however it doesn’t necessarily have to physically connect to the battery ground point.

Avoid choosing ground points that are secondary body or chassis components that may have the added resistance of tack welds or bolts between the main and secondary parts.

Avoid choosing ground points that share connections with other vehicle accessories. This helps avoid potential noise problems from the start.

All ground washers shall be star washers. Flat washers are not ideal for grounding. Flat washers can trap contaminants between themselves and the grounding surface, which increases contact resistance. Star washers tend to bite into the grounding surface this cleaning it and getting more surface area for lower contact resistance.

Audio System Guidelines

All power and signal leads should be run away from each other to prevent noise in the audio system.

All wiring should be run away from the vehicles factory wiring due to the fact that these high-current wires can induce noise into the system.

Ground loops are the most common cause of noise in an automotive audio system. Ground loops result when all the components in an audio system do not see exactly the same ground.

High quality signal cables will be used if the computer is going to be hooked up to an audio system. This is to prevent any interference issues with the signal path.