Automotive electrical-system...
Automotive electrical-system wiring is color coded for easy identification. This makes short work of finding lead origins and destinations. When creating your own wiring, say for a stereo or electric-fan install, use multiple wire colors and draw a diagram. It will help in the future for repairs or wiring changes.
Trouble Shooting Electrical Problems
Although a lot of us are mystified by electrical-system woes, most are easy to troubleshoot and understand. Marvin McAfee at MCE Engines has a straightforward approach to trouble-shooting just about anything. He suggests starting with the most obvious stuff first. If the bulb won't light, is it burned out? Is there power to the socket? Check the bulb first. Check the fuse. Don't always assume the worst when something quits. Most of the time, it is something like a dead battery, a burned-out bulb, or a failed switch. Rarely are electrical system failures wiring related-most of the time, it's component failure.
When something electrical quits, determine what else is working and what isn't. If everything in the vehicle is dead, begin your troubleshooting at the battery. Never assume because you just came off the road or because the battery is brand-new that it is fully charged. Examine battery cables for corrosion or loose connections. Check the battery's negative ground at the engine block. Check the ground strap between the engine and firewall. This is all common sense stuff, but you'd be surprised how many miss it, including us.
Headlight switches and circuits...
Headlight switches and circuits are protected with a circuit breaker inside the switch. Circuit breakers are used for safety because they don't completely break the circuit should a short occur. They cycle the headlamps off and on. Also in the headlamp switch is a variable resistor to control instrument lighting.
Classic Ford electrical systems are all similar. Wiring color codes are virtually the same across all models and years. For example, instrument lights are blue with a red stripe on Mustangs, Galaxies, Falcons, Fairlanes, and F-series trucks. The same can be said for left and right turn-signal indicator lamps, high beams, taillights, backup lights, headlamps, heater-fan wiring, and the rest of it. All have the same color-coding regardless of carline type. This makes short work of troubleshooting when you know what it all means.
Ford electrical systems have two basic sources: power direct from the battery and switched-power from the ignition switch. The latter is live only with the ignition switch in the "on" or "acc" position. Items like brake lights, emergency flashers, horns, courtesy lights, headlights, instrument lights, and the cigarette lighter are live all the time, protected by fuses or circuit breakers. Turn signals, the heater fan, the radio, the transmission indicator light, the windshield wipers, and other accessories get power from the ignition switch, also protected by fuses. This is important to know when any of these items quits.
This is a variable resistor-a...
This is a variable resistor-a coiled stretch of resistance wire designed to increase impedance (resistance) as we dim the lights. The solid contact turns on the courtesy lights.
Any time electrical components quit operating, you need to determine if they are getting power to begin with. Check the fuse first. When in doubt, replace the fuse before doing anything else. Sometimes a fuse can be blown at either end of the filament and appear to be good. The same is true for light bulbs that don't look burned out. Sometimes there's only a tiny break in the filament not visible to the naked eye. Some offshore light bulbs can suffer meltdowns of the filament towers, causing internal bulb shorts and fried wiring. You can also check the fuse or the bulb's integrity with an ohmmeter. If there's no continuity through the fuse or bulb, it is bad.
Fuse boxes get power from...
Fuse boxes get power from two sources-the battery and the ignition switch. Switched power happens when the ignition switch is on. Direct battery power is available all the time, straight from the positive side of the starter solenoid.
Switched power comes off this...
Switched power comes off this post on '65-'67 Fords. For '68 and '69 models, power is internalized in the interest of safety. From 1970 up, Ford used a linear switch located down low on the steering column. All wire color coding is the same, in any case.
Prior to 1967, firewall connections...
Prior to 1967, firewall connections were made like this at the firewall. In 1967, Ford moved these critical connections inside the vehicle under dash. This made them less vulnerable to corrosion and failure.
One of the biggest wiring...
One of the biggest wiring gremlins people seldom catch in troubleshooting is negative ground connections. When electrical grounds are weak, all kinds of oddities occur because there isn't a sufficient ground. Sometimes one headlight glows faintly without the headlight switch turned on. This means something is grounding through the headlight to ground, causing the filament to glow. Sometimes this will happen via a turn-signal lamp or instrument lamps. Make sure there's a ground connection between engine and firewall to ensure proper ignition and charging system operation. Check all grounds thoroughly.
Gang or multiplex plugs like...
Gang or multiplex plugs like this one make light work of multiple connections. Power always comes via the female connections, with male connections being the receivers.
Single and duplex plugs like...
Single and duplex plugs like these work the same way as the multiplex plug just mentioned. Females provide the power. Males receive power. Follow your Ford's wiring diagram for specifics and follow color codes.
Any time you see "resistance...
Any time you see "resistance wire," this means do not cut. What's more, do not use the resistance-wire connection for anything but the positive side of your Ford's ignition coil. Resistance wire means there is less voltage at the receiver.