Another alternator charging question...
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Freshman User
Joined: May 2005
Posts: 26
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Another alternator charging question...
My son and I have an 72 f250 that we've been working on. Problem was the battery going dead, the old owners always had a charger plugged into it when they parked it. I put in a new battery, checked the voltage when running and it was at 12, bad alternator I thought. Went to Autozone to check, and they said that the alt was bad, volt reg good, but had something about checking "wire" to the alt. Suggested I pull the alt and have it checked by itself. Went home, pulled the alt, took it back and it checked okay. Bought a new volt reg, they suggested/I bought a new fuseable link and went back home. When I was putting in the new volt reg, I noticed that the harness wasnt even plugged into the old volt reg...crap, so how did it read okay on their meter? So hook everything back up, old alt, new reg, fuseble link, even went over every wire. The heavy wire to the alt had a gouge and broken strands so i put in a butt splice, still no charge at the battery! All I can do now is replace the alt, its only 40 bucks but is there something else I'm missing? The gauge in the truck shows no charge, but it does slightly move to discharge when I use the lights, turn signals. Can I hook up voltmeter somewhere else to check out my harness/reg/alt on my own?
Thanks
Thanks
Fleet Owner
Joined: Aug 2005
Posts: 23,668
Likes: 301
From: Easton,Ks
Check to see if you have 12V on the BAT. Terminal of the Alternator before you start it.
If NO check continuity from the BAT. Terminal of the Alternator to the + side of the Battery.
If it is infinity you have an open in your 38 BK/R or BK/O Wire.
Start Engine.
Check for 12V on the Field wire.
If yes you have a bad Alternator.
If NO momentarily jumper 12V from the BAT terminal of the Alternator to the FLD. terminal and see if it will charge.
If YES you have a bad Regulator or bad Field wire coming from the Regulator or no 12V on the "A+" terminal of the Regulator.
Also check to see that you have 12V on the "S" terminal of the Regulator with the key on.
Note wire colors may differ.
If NO check continuity from the BAT. Terminal of the Alternator to the + side of the Battery.
If it is infinity you have an open in your 38 BK/R or BK/O Wire.
Start Engine.
Check for 12V on the Field wire.
If yes you have a bad Alternator.
If NO momentarily jumper 12V from the BAT terminal of the Alternator to the FLD. terminal and see if it will charge.
If YES you have a bad Regulator or bad Field wire coming from the Regulator or no 12V on the "A+" terminal of the Regulator.
Also check to see that you have 12V on the "S" terminal of the Regulator with the key on.
Note wire colors may differ.
Last edited by subford; Oct 7, 2005 at 11:01 AM.
Moderator
Joined: Jan 2001
Posts: 57,025
Likes: 2,756
From: Virginia
From your post let's assume the alt is good, since it checked good, and the reg is good, since it's new. I would go over the wiring very carefully. It would probably be a good idea to un-wrap the harness going to the alternator. The heavy output wire has a splice in the harness, and some guys on here have found that area corroded.
If you have just painted the engine compartment, you may want to also check and make sure the regulator has a good ground, and you have a ground strap installed between the engine block and the sheetmetal. The engine is mounted in rubber mounts, so you need some ground straps.
If you have just painted the engine compartment, you may want to also check and make sure the regulator has a good ground, and you have a ground strap installed between the engine block and the sheetmetal. The engine is mounted in rubber mounts, so you need some ground straps.
