Introduction . . . Automotive trouble-shooting combines diagnosis and repair. It takes you step by step irom the condition in need oi correction, to the cause, and to the repair action. Through the logical stepped" approach, repairs can be achieved quickly and accurately. This manual covers trouble-shooting ol the electrical and vacuum systems in 1979 Ford F-1OD/350 Truck and Bronco vehicles. It utilizes easy-to-iollow graphically-specific schematics and systems drawings. Like others in the series. it is designed to be used by the occasional and "advanced" do-it-yourselier. All diagnosis and repair can be conducted With common electrical and vacuum toolsno special. or unusual, tools are required. Repair procedures. wiring colors. connectors and locations listed in this manual have been checked on production vehicles. However. changes in wire color, connector locations, etc. may be made during the model year, lfyou should encounter this. note the variation in the section covering that system to enable you to keep your manual accurate. Preliminary to any repair or diagnosis related to the electrical system. be certain that the battery is in the proper state of charge How to Use this Manual . . . This manual covers basic electrical and vacuum trouble-shooting procedures tor 1979 Ford F-100/350 Truck and Bronco vehicles, it uses a briel "condition/step" approach to guide you through the trouble-shooting procedures. That is, you are given the lF. . .If the voltmeterreadingi's zero . . and the ACTION , . .repair the lead to the component, The intent of this manual is to help you track down the cause of covered conditions and once youve located the cause, what corrective action to take, It does not, however, tell you how to repair and adjust the suspect components in most cases. liyou need help in this area, refer to the 1979 Ford Light Truck Shop Manual. You can order it on the same form you used to order this. Naturally, as an electrical and vacuum troubleshooting manual, this publication relies heavily on schematics. To make the schematic as simple as possmle. graphic symbols have been used to represent key components or parts.lnstead oi the wiring diagram of an alternator youll see a picture. The same is true of the regulator and other items where internal circuitry doesnt al'lect trouble- shooting. ln components where in- ternal circuitry is important to trouble shooting awiring diagram may be shown in combination with the graphic. Special Symbols/Color Designations SYMBOL DESIGNATION PC Printed Circuit s Splice G Ground COLOFI DESIGNATION Black bk Brown br Dark Blue db Dark Green dg Gray 9y Light Blue lb Light Green lg Orange 0 Purple 9 Pink pk Fted r White w Yellow y When two colors are indicated tor a wire. the rst color is the basic color of the Wire, the second color indicated is that of the auxiliary markingdash, hash or stripe. Wires with dash markings are shown by a D. Hash markings with an H. lino markings are shown the auxiliary marking is understood to be stripes. Examples: bk/lg H is a black wire wtth light green hash marks. r/y D is a red wire with yellow dots. br/o is a brown wire with orange stripes. Contents Air Conditioner (Electrical) .. ,. . . . . 39. 41 Air Conditioning (Vacuum) . ..... 39, 42-44 Accessories ., .. 31, 32, 34, 36, 38 Backup Lights .12, 19, 22 Brake'ransmission Vacuum Supply .... . . .,.. , 46 Brake Warning Lights Carburetor Vent Solenoid . Cargo Light . . Charging System . Cigar Lighter . , . Control and Instrument Lights . . Courtesy Light . .. . . . . Emergency Warning Light . . Exterior Lights . . . FogLights . ...., 4-Wheel Drive Indicator Lights . Fuel Gage . , , . ..... . Fuse Block . . . Glove Box Light , . . Heater/Blower . . . . 39. 40, 43 Heating System 5. NC . . . ..39, 40, 43 Horn ,,,,,,,,,,,,,,,,, . , . .32, 33 ignition ,,,,, ., . , . 5, 10,11 Instrument Cluster Volta . interior Lights . ..... Lights . . . . ....... . Alternator Warning . . Backup .. .. Brake Warning ,,, , Control . Dome ...... Glove Box . . . Headlights License . Map . . . . Side/Hoot Marker . Oil Pressure Warning . ... Seat Belt Warning Stop ............ Turn Signals .. .. 12, 20-22 Oil Pressure Gage . ,. ,.... . . 27, 31 Oil Pressure Warning Light . , . , . . 27-29 Parking Lights ....... . 12, 15-17 Power Distribution. ...5, 8, 9 Power Tailgate .. . . .32, 38 Radio . ,3 ,34,35 Reminder uzzer .. , . . 12. 27-29 Seat Belt Warning Light . . 27. 28 Speed Control ,,, . ,. 32. 47 Start/ignition .. . ,... 5. 10, 11 Stop Lights . . ,, ... 12, 20-22 Temperature Gage . . 27, 30, 31 Throttle Solenoid Tools, (Electrical) Tools, (Vacuum) . Trailer Circuitry .. Trouble-Shooting. Basics ,, Turn Signals H, . Vacuum Systems . ,,.. 44415 Vanity Mirror Lights .,.....H .. 14 Warning Lights 8. Gages . , , . 27, 28 Windshield Washers/Wipers ........... .32, 36. 37