I have a 79 F150 with a 351M. I put a few electric fans on it and wanted to upgrade the alt. I bought a 100amp from LMC for $100. Its different then the one on the truck. I expected some differences...maybe fewer posts ect but not what I found. The one on my truck is a three post on the rear of the alt.(standard 65amp stock alt) with a the voltage regulator mounted on the firewall. The alt that LMC sent me is a 2 post side connection. and it also has a hole in the side where it looks like a voltage regulator should plug in and mount on the alt. I checked the part number on the box and compared it to what I ordered and everything matched. I went to advance auto and they showed me two diff alts. the stock 65 amp was rear post setup. there upgraded version was a 70 amp that had the same side hook ups as the one i received. (BOTH are supposed to be direct bolt on stock replacements!!!!) I bought the stock one (65amp) and threw it on there not wanting to fry everything. I know its not going to last long pushing 3 fans in the heat down here in So FL so I need to upgrade.

Any suggestions...should i try to put all 3 stock wires on the pos post and not worry about the hole on side with that weird plug...or return it and buy an expensive single post alt...or anyone have any other CHEAP options??? Everyone knows how tight times are now....

Thanks Guys,
Cody

 

Oh and the 100 amp alt from LMC came with a test sheet stating it was a 12v/70amp alt. Apparently they rewound it to push more??? It tested at 81amps max output...incase that helps.

 

I don't know I never seen the alt with the side ter. you where talking about I 'll check it out, but I did the same thing you did, I have 3 elct. fans and they just kill the stock alt I just got a 3rd gen. alt. like what was on my 92 mustang the housing is the same so the mounts are the same and you can get a custom harness to hook it up I just got mine installed and I can not pull that thing below 13.5 volts with high beams, wipers, heater, fans, and stereo on I got it from a company called quality power good tech support too

 

Ford offered a 100 amp alternator on 1977/79 F100/350's & 1978/79 Bronco's with 351M/400's, but the adjustment arm is different due to the larger size of the alternator.

In the mid 1980's Ford began using an alternator with a built in regulator. These alternators were not used on 1970's anything.

 

Bill,
Saying that the adjustment arm is different... Does that mean that the alternator will still be a direct bolt on if one has the smaller one already ? Thanks!
Dak

 

Go 3g, that's what I did. 130 amps at a budget friendly $35 bucks at the J/Y. Pulled mine form a '89 Sable with a 3.8, bolted right up on my 400 like it belonged there. Changed the pulley and the wiring wasn't hard at all.



There are a ton of write ups on how to do it.

 

codyingersoll123 if there is a substantial size difference in the size of the case of the 70 amp alt they could have given you a large case alt that came on the cars like LTD's and galaxies that would not fit the brackets for the small case alt thats on our trucks you could switch brackets but thats going to screw up pulley spacing and probably have to change all ***. brackets. I have screwed around with other set ups and I am very pleased with this 3rd gen. set up go with it you won't be disapointed it fits your brackets and is made for the demands of all the electronics of the early 90's I can finally run my 3 fans at night driving in the rain on a cold day and still crank the radio.

 

Yep, when I went 3g I noticed right away that my stereo sounded better (it's a BIG stereo ), and the headlights were noticably brighter.




In fact, if you pay attention, a lot of the alternator upgrades that you see (even for non-Ford vehicles) are the 3g FoMoCo alternators.

 

I bought my alternator new from a place, its reworked so it puts out 95 amps at idle, but if you know your part #'s you can get a really high output alt. from the junkyard. I was surprised when I saw the mounts have not changed and the wiring is the same, it just looks different. It took my alt. going out on my 92 mustang to get me started on the idea

 

If the alternator is from the 1970's, yes. The only thing different is the adjustment arm.

After 1979, I dunno.

 

Just an FYI - "95 amp alternator" doesn't mean it's continuously pumping out 95 amps at idle. Alternator output is a function of the load on the vehicle's electrical system, as determined by the regulator. Saying an alternator is "95 amps" just means the alternator itself can handle producing that much current without burning itself up. Additionally, it's very unlikely any alternator can produce anywhere near its current rating at idle. Alternator output is directly a function of the rate of change of magnetic flux in the stator, which essentially means that the faster the alternator is spinning, the more current it can produce (rotor spins faster, flux changes more rapdily, rate of change increases). It's called Faraday's Law. The reason I'm saying all this, is don't be enticed by alternator rebuild shops into spending more money when they say stuff like that.

The purpose of an alternator is not to throw as much juice at the battery as possible. It's simply part of a system that keeps the vehicle's electrical system at around 13.5 volts. The vehicle's charging system is a feedback loop. It only makes what it needs.

 

Yes I understand everything is based off of the ***. calling for the power and I have to say I beleive it can put out that much at idle.

 

What do you mean? The alternator's maximum current rating has to account for the current it delivers when it's spinning at its highest RPMs. Therefore the current output at idle must be lower. If your 95 amp alternator literally put out 95 amps at idle, it would blow itself up when you rev your engine. Unless you've actually measured the alternator output at idle, you cannot say it does. But I don't recommend trying that.

I'm not saying your alternator is not capable of producing 95 amps. I'm pointing out that through simple physics (Faraday's Law), your engine isn't rotating fast enough at idle to push the alternator to its current limit. Furthermore, it's unlikely your voltage regulator even calls upon the alternator to output that much current at idle assuming you're not running 14 inch subs and a winch sitting at a stoplight with the AC on full blast.

Once again: vehicle charging systems are not a constant all-or-nothing system. It's a feedback loop. The alternator is only allowed to produce what it needs. As soon as the regulator sees the voltage on the A+ terminal go to around 13.5 volts, it shuts off the field. As soon as it drops, it switches it back on. It's a back-and-forth process to maintain a constant voltage, which is why the brain of the system is called a regulator.

 

I was just trying to saying that with the engine at idle (750 rpm) I tried to run everything posible and this alternator kep up with maintaining 13.5 volts. The stock alt. could not. I did go through the ford service procedure to check if it was functioning properly, it passed all tests except for load. I tried different alts but they did the same thing they were off other vehicles that seemed to worked fine. Yeah It would take a really big ammeter to measure at that amp rating to see what its putting out, Ill take there word for it, it works. It was more expensive than a auto zone alt. but cheaper than if you got one from the ford dealership so I'm happy with it.

 

OK im guessing by 3G you all mean 3rd gen ford vehicles??? Some one said 89 sable...what other trucks or cars can I get them off??? Which ones have the higher amps?

Just to make sure I understand everyone correctly.... if I get a 3g alt all I have to do is swap the pulley and it will bolt right in??