auto wire

7/28/2019 Auto Wire

1/3

EL-22 June 5, 1997

[Filename: AUTOWIRE.DOC]

Automobile Wiring Harness

Contributor: David H. Cowling

Affiliation La Tech University

Address: Electrical Engineering

PO Box 10348 T.S.Ruston, LA 71272

Phone: (318) 257-2857

Fax: (318) 257-4922

Email: [email protected]

Type: Design Project

Student Time: Two to Four Weeks

Location: Classroom, Library, Home

Summary

Wiring harnesses for automobiles (or for that matter most mechanically powered vehicles)

can be highly complex. There are large numbers of factors that go into their makeup.

One must provide for power (i.e., current) for each electrically operated device on the

vehicle. However, one must also provide control for each of these electrical devices.

Safety also enters because if something goes wrong with any device (or incidentally the

wiring harness itself) then current and hence power may climb to destructive levels. This

can lead to wires fusing together in the harness, insulation catching fire and ultimately a

vehicle fire.

Under this design a wiring harness and electrical control system for a vehicle are to be laid

out. This should include meeting the requirements of power distribution, total energydistribution, control, and finally safety for a mechanically powered vehicle. This vehicle

should be equipped with a reasonable number of amenities (would you actually purchase

one of these). This vehicle should also meet the required safety standards (i.e. headlights,

taillights, stop lamps, turning signals, windshield wipers, windshield washers, horn, seat

belt warning, and other signals and indications both of engine performance and safety.

ABET Descriptors

Engr Sci Content: Electrical, Electrical Power, Electronic

Type: Component

Elements: Establishment of Specifications, Synthesis, Analysis, Evaluation

Features: Design Methodology, Creativity, Open-ended, Modern Design

Theory

Constraints: Reliability, Cost, Safety, Manufacturability

Effort: Team

7/28/2019 Auto Wire

2/3

EL-22 June 5, 1997



Under this project a small design group should layout and design a complete wiring

harness for a mechanically powered automobile. This harness should be arranged to

power all the features (including the mandated safety features found on an automobile

(such as one you would buy). The project should start with a careful examination of the

electrical features desired, should continue with a decision on the method of control,

followed by a schematic, a wiring diagram and finally the analyzed design of the harness.

Wire size, insulation and color code must be specified. Derating of the wire size and

insulation should take place based on the method of cabling the harness.

The completed design should include but not necessarily be limited to:

The electrical specifications for the vehicle.

A schematic diagram of the electrical system.

A wire routing diagram.

The number and routing of the separate sections of the wiring harness.

The type of cabling for each of the sections.

A specification (wire size, insulation, and color code) for each wire in each

section of the wiring harness.

7/28/2019 Auto Wire

3/3

EL-22 June 5, 1997



Objectives/Comments:

This project should cause a team of three or four students to investigate the specifications

of the electrical requirements for an automobile. It will require analysis on the students

part of the required wire sizes. When cabling is examined wire size may need to be

derated. Notice that derating for flat cables would be different from that for round,

enclosed cables. This project should also promote some thought on the way to best

handle the circuit breaker and fusing requirements for safety. Examples may be made of

various US automobile manufacturers versus some of the earlier English (Triumph, MG)

manufacturers.

Engineering Notes:

The cabling of an automobile may be a weak link. Students will be surprised at the

amount of current that is required for simple circuits (for example brake lamps). The wire

must be sized in a harness to carry the required current without overheating. If excessive

voltage drop occurs electrical devices may work poorly or not at all. The placement of

the safety features (circuit breakers, fuses) in a harness is very important. Do not forget

the placement fusible links. Some English automobiles (Triumph, MG, Midget, etc.) were

built through the 70s without fusible links and the results were disastrous for wiring

harnesses in those automobiles.

Finally, the students may wish to completely depart from conventional methods of

handling the power distribution and the control of the electrical systems. Examples of

such departures would be a multiplexed signal bus and a single large power bus. Decoders

could be employed to activate the various electrical components from digital codes

contained on the signal bus.

Expected Outcomes:

Students will become aware of the effort that is required to implement the main electrical

circuits of devices that they may think of as mundane. They should develop a new

appreciation for the work and effort to design such a system. This is an opportunity to use

knowledge that they are acquiring in circuits and apply this to the real world.

auto wire

Documents