Correct Alternator
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Senior User
Joined: Sep 2001
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From: Friendswood TX
Correct Alternator
It is hot now in Houston, and I run the A/C flat out every chance I get, but I don't know if I have enough alternator to keep the charge going to the battery as well as the mucho amps the fan motor draws (wires get hot). Any suggestions as to what I should have for the size of alternator? I drove from work the other day, about 7 miles from the office to the post office, and she wouldn't crank after I shut her down. 390 2 BBL... 
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Most 73-79 trucks came with either 61 or 70amp alternators, but some models were equipped with 90 and 100amp units. I retro-fitted a brand new (Bosch)100amp alternator (6.5 inch case) into my F100 (originally with a 61amp unit, 5.25" case) a few months ago with no problems.
A nice Ford feature is that all these alternators use the same voltage regulator. Only changes needed were a slightly longer belt and changing two out of the three terminals in the wiring. Now I can feel confortable with the current demands of my stereo system and fog lights, and I am seriously considering adding an A/C system soon (I also live in hot Texas-Dallas). Raul
A nice Ford feature is that all these alternators use the same voltage regulator. Only changes needed were a slightly longer belt and changing two out of the three terminals in the wiring. Now I can feel confortable with the current demands of my stereo system and fog lights, and I am seriously considering adding an A/C system soon (I also live in hot Texas-Dallas). Raul
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Vans and 79 PU's could have 100 amp alternators
PU's with the contractor package got High out put alts.
Most pickups between 1973-75 could have 38,42,55,61,amp alts
78's could have 40,60 ,60 calif,70 & 90 amp alts
79's could have 40,60,65,70,100 amp alts
PU's with the contractor package got High out put alts.
Most pickups between 1973-75 could have 38,42,55,61,amp alts
78's could have 40,60 ,60 calif,70 & 90 amp alts
79's could have 40,60,65,70,100 amp alts
Last edited by Mil1ion; Jul 26, 2006 at 04:04 PM.
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From: Calgary Canada
If the wires are getting hot from the amount of current you are drawing, you ought to consider putting in some larger wires. Could also be a sign of something not operating correctly. Ford would not have designed anything to run this way.
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I forgot to mention that when I did my 100amp alternator upgrade (on '78 with 6- inline engine), I also did upgrade all cables to 2 gauge (overkill, but I found a long roll on clearance at RadioShack) and new battery gold-terminals (also on clearance).
The upgraded cables were -Battery to chassis, +battery to alternator (with a 100 amp fuse close to the battery), -battery to engine block and chassis to engine block. I think they call this the big 3 (cable) upgrade. So no cable overheating issues. Raul
The upgraded cables were -Battery to chassis, +battery to alternator (with a 100 amp fuse close to the battery), -battery to engine block and chassis to engine block. I think they call this the big 3 (cable) upgrade. So no cable overheating issues. Raul
Last edited by superbepro; Jul 26, 2006 at 05:11 PM.
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It will be stamped on side of alternator as Mil1ion mentioned with either 40A, 60A, 65A, 70A, 75A, or 100A amp alternators. The letter A represents Amperage. It will also have other numbers and letters stamped nearby the ##A.
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From: SD
Originally Posted by Boltgunner
I don't know if I have enough alternator to keep the charge going to the battery as well as the mucho amps the fan motor draws (wires get hot)...7 miles from the office to the post office, and she wouldn't crank after I shut her down.
I suspect a bad starter. When the starter gets old and worn, the windings are weak and require more amperage when hot. So when the engine is good and hot, then you shut it off for 5-10 minutes, then the starter cranks slowly. But once the starter motor is cooled off, it cranks fine. My '73 390 goes through a starter every 3 years or so - but I have headers which shortens the life of the starter due to excess heat - but then again you live in Texas, lots of excess heat there too...
Marty
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Hot fan motor wires are usually caused by bad connections on the wires, typically at the blower speed resistor module. Replacement connectors can be purchased from appliance dealer service departments. They are made of a special alloy specifically for heater elements in electric dryers. Do not use the standard crimp connectors from an auto parts store.