Circuits

Automotive circuits are divided into three categories: power, signal (control or data), and ground circuits.


POWER CIRCUITS

Power circuits are classified as those cables that provide battery or mechanically switched battery voltages to electrical loads. Some examples of these circuits are:

^ Ignition circuits - 202, 102A

^ Battery circuits - 1A, 1B

^ Headlamp circuits - 40, 40A, 40B, 40C

^ Defog circuits - 193,1240, 293, 293A

SIGNAL (CONTROL OR DATA) CIRCUITS

Signal circuits are classified as those cables that provide signal voltages from one electrical device to another device. Examples of these signals and devices are:

^ Canister purge solenoid to PCM - 428, 428A

^ Fuel sender to fuel gage - 30, 30A, 30B, 30C

Signal wires are usually current limited by one of the devices that is attached to the wire. In the above examples the PCM and fuel gage limit the current in these circuits through the use of electronics (pull up or pull down resistors, transistors, etc.). Signal wire current levels for short circuit conditions normally do not exceed operating levels by an appreciable amount.


GROUND CIRCUITS

Ground circuits are classified as those circuits that provide a ground (zero voltage level with reference to the battery) to the electrical system. Examples of these circuits are:

^ General IP ground - 350

^ PCM ground - 551

Since ground circuits are already shorted to ground, the current level is based on the electrical load resistance. Like signal circuits, ground circuit cable selection is a function of operating current.