I fought this same problem with my daughter's 99 F250 last summer, having the alternator rebuilt and buying a new one from NAPA. NAPA's alt test machine showed the fresh rebuild to be bad, so on Monday I took it back to the rebuilder and he tested it proving it would put out 120 amps. He did the tests right in front of me, and laughed when I told him the NAPA alt tester story. He said "sure they want to sell you their $100+ alternators (reman in Mexico)".
With much frustration, and encouragement from the alt rebuild guy, I kept digging until I found the problem in the factory wire harness beneath the batt box on the right side fender. Either batt acid or road salt had gotten into the covered harness and got to the junction where the 2 fusable links, the big alt output wire and the one small wire that feeds back to the alt plug. The small copper wire was down to about 2 small strands and a lot of green copper dust. The voltmeter would read 12 V, but it could not carry enough current to excite the alt. Trimming all wires back to solid copper and soldering them together and taping the heck out of it made everything work correctly. I had nearly pulled the dash wiring apart trying to find the problem there.
Don't trust a good looking wire harness. I spent days trying to find the problem. Alt rebuild guy said Ford PUs have this problem somewhat commonly. An easy test to prove your wire harness is OK is to use a spare 12V headlight bulb with 2 test leads. Hook one lead from bulb to ground, and the other from bulb to the unplugged wire harness side of the alt plug with the ignition switch turned on, engine off. One of the small wires in the plug is switched by the ignition switch, the other one is a back feed from the battery (through the possibly offending wire harness). The headlight bulb limits the current to about 5 amps, so the small gauge wire is not injured. In this test I have described, both small wires (each separately) in that connector should fully light the bulb. If the bulb lights with both wires, the dashboard side of the circuit is OK, and the wire harness going to the fusable link is OK. If I had known of this test, I would have saved a lot of time and $$$.
We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]
Today's Featured Article - Show Coverage: Journey to Ankeny - by Cindy Ladage. We left Illinois on the first day of July and headed north and west for Ankeny, Iowa. Minus two kids, we traveled light with only the youngest in tow. As long as a pool was at the end of our destination she was easy to please unlike the other two who have a multitude of requirements to travel with mom and dad. Amana Colonies served as a respite where we ate a family style lunch that sustained us with more food than could reasonably fit into our ample physiques. The show at Ankeny
... [Read Article]
Latest Ad:
1964 I-H 140 tractor with cultivators and sidedresser. Starts and runs good. Asking 2650. CALL RON AT 502-319-1952
[More Ads]
All Rights Reserved. Reproduction of any part of this website, including design and content, without written permission is strictly prohibited. Trade Marks and Trade Names contained and used in this Website are those of others, and are used in this Website in a descriptive sense to refer to the products of others. Use of this Web site constitutes acceptance of our User Agreement and Privacy Policy
TRADEMARK DISCLAIMER: Tradenames and Trademarks referred to within Yesterday's Tractor Co. products and within the Yesterday's Tractor Co. websites are the property of their respective trademark holders. None of these trademark holders are affiliated with Yesterday's Tractor Co., our products, or our website nor are we sponsored by them. John Deere and its logos are the registered trademarks of the John Deere Corporation. Agco, Agco Allis, White, Massey Ferguson and their logos are the registered trademarks of AGCO Corporation. Case, Case-IH, Farmall, International Harvester, New Holland and their logos are registered trademarks of CNH Global N.V.