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Search Auto Parts Search 1978 f100 not charging, new battery & alternator Sign up here!   Email This Post Auto Repair Home>> Automotive Repair>> Automotive Wiring and Electrical chincoteaguer Novice Feb 13, 2014, 9:46 AM Post #1 of 5 (2843 views) 1978 f100 not charging, new battery & alternator Sign In 1978 F100, 6 cylinder 300, four speed, power steering, no a/c, 179,000 miles. Alternator light illuminated at slow speed. Light goes out when engine is at high speed. Battery goes dead after few days use locally on farm. Installed new battery ( old one was 4 yrs + old). Installed new alternator (advice from local NAPA dealer). Problem still remains. I'm thinking this may be a grounding problem and intend to clean all connections but with my limited experience I can not rule out worn out wiring. Any suggestions out there? Ernie nickwarner Veteran / Moderator Feb 13, 2014, 10:34 AM Post #2 of 5 (2829 views) Re: 1978 f100 not charging, new battery & alternator Sign In This has an external regulator on the firewall or inner fender. Looks like this. If it gets moisture in it or in the connectors of the wires going to it you can have a poor charging issue. Try this for a test. Locate the regulator stud on your alternator. Put a multimeter on your battery to watch the voltage. Now run a small jumper wire from battery positive to the regulator stud. If the alternator and the cable between it and the battery is good you will see the voltage spike up. Take off the jumper, you don't leave it that way or it will severely overcharge because it is maxing the alternator out. Then you need to be looking at the regulator and its related wiring. The connectors at these were not sealed weathertight and are prone to this issue, also the casing of the regulator wasn't made weathertight either. Common on these older trucks but the good news is these parts are cheap and you have plenty of room to work. Make sure you are coating all the electrical connections with dielectric grease after you clean them to hold off the corrosion in the future. Hammer Time Ultimate Carjunky / Moderator Feb 13, 2014, 12:45 PM Post #3 of 5 (2824 views) Re: 1978 f100 not charging, new battery & alternator Sign In Or you could use one of these........ I still have one ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional. Tom Greenleaf Ultimate Carjunky / Moderator Feb 13, 2014, 12:46 PM Post #4 of 5 (2823 views) Re: 1978 f100 not charging, new battery & alternator Sign In Yup. Separate regulator. Problems have included the plug harness or that regulator. Double check me but it should spike voltage if you ground the MARKED terminal "F" for field and like Nick just said do NOT leave it that way, just tells that alt can put out. Caution as that spike can blow light bulbs so just as fast as you can, everything powered off, T chincoteaguer Novice Feb 13, 2014, 5:28 PM Post #5 of 5 (2800 views) Re: 1978 f100 not charging, new battery & alternator Sign In Thanks guys. Nice to have such expertise. Will execute diagnosis as soon as this weather breaks. Will post results. Ernie   Email This Post   Automotive Repair     Auto Body Repair and Refinishing     Heating or AC Issues     Electrical and Wiring     Brake Systems     Car Stereo Repair Advice     General Discussions     Car Making Funny Noises     Engine Fault Codes     Engine Troubles     Exhaust Systems     Steering and Suspension     Transmission Troubles     Tricks of the Trade Automotive World     General Discussions     Antique Car Talk     Car Shows and Events     The Bargin Bin     Motor Vehicle Inspection     Car Care Tips     Traffic Tickets     Gasoline, Motor Oils, Concept Cars and Engines     Auto Insurance, Financing, Leases, Warranties Truck Repair     General Discussions     Truck Engine Repair     Truck Suspension Repair Motorcycle Repair     General Discussions     Motorcycle Engine Repair CarJunky     Open Posting     Board FAQ's     New Board Suggestions

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