Alternator ISSUES!

crankywanker · Mar 3, 2011

Hey all, I have a 1969 mustang with a 351 Cleveland 2v smushed inside the engine bay. The problem is I am using an alternator that was attached to my 302 and worked fine back then. However, I have an MSD-6AL on the 351 cleveland and an electric fan as well. I'm guessing that this is draining the power because my battery dies after about 30 minutes or so. So with a brief history, I had my 1969 mustang with a 302 and 3.00 gears and a C4 Tranny. I swapped out the gears for 4.11s and blew the 302. I then purchased a 351 cleveland full hydraulic roller. It's a great engine! I bolted it up to my C4 and now the car is great the only problem I have is with my alternator and a major leak on the C4 transmission(which I am going to be looking at in the near future). However, the Alternator really has me down because I keep looking for a source to buy a new high output alternator and I just cant find one. Thanks for any help.

robbz28 · Mar 3, 2011

Go to your local parts house (oreilly or what have you) and get a 65 amp three wire alternator, should cost you around 50 bucks. I have one on my 67 with a/c, electronic ignition, electric fan, sound system, and all the other bells and whistles and it works great. Get a three wire like the original because they are way better than 100 amp one wires. The one wires only charge the battery, that is all they do, the three wires charge the battery AND power your accessories. If anyone tells you a one wire is better then ask them why they dont use them on cars built today. They do serve a purpose, but I feel any driver needs to have OEM style alternator.

PoppyMod · Mar 4, 2011

crankywanker said:
Hey all, I have a 1969 mustang with a 351 Cleveland 2v smushed inside the engine bay. The problem is I am using an alternator that was attached to my 302 and worked fine back then. However, I have an MSD-6AL on the 351 cleveland and an electric fan as well. I'm guessing that this is draining the power because my battery dies after about 30 minutes or so. So with a brief history, I had my 1969 mustang with a 302 and 3.00 gears and a C4 Tranny. I swapped out the gears for 4.11s and blew the 302. I then purchased a 351 cleveland full hydraulic roller. It's a great engine! I bolted it up to my C4 and now the car is great the only problem I have is with my alternator and a major leak on the C4 transmission(which I am going to be looking at in the near future). However, the Alternator really has me down because I keep looking for a source to buy a new high output alternator and I just cant find one. Thanks for any help.

I'm assuming you load tested the battery and check the output of the alternator? One, or, the other failed?

crankywanker · Mar 4, 2011

PoppyMod said:
I'm assuming you load tested the battery and check the output of the alternator? One, or, the other failed?

my voltage meter slowly dropped down from 14-10.

crankywanker · Mar 4, 2011

robbz28 said:
Go to your local parts house (oreilly or what have you) and get a 65 amp three wire alternator, should cost you around 50 bucks. I have one on my 67 with a/c, electronic ignition, electric fan, sound system, and all the other bells and whistles and it works great. Get a three wire like the original because they are way better than 100 amp one wires. The one wires only charge the battery, that is all they do, the three wires charge the battery AND power your accessories. If anyone tells you a one wire is better then ask them why they dont use them on cars built today. They do serve a purpose, but I feel any driver needs to have OEM style alternator.

I'm curious, is this three wire going to be the same as say my current alternator that is for a 67 mustang with a 302? I suppose it will be but perhaps it is bad and needs to be replaced anyways. Okay well thank you good sir! this gives me hope that the alternator will be able to handle it.

crankywanker · Mar 4, 2011

thank you robbz28 and poppymod!

PoppyMod · Mar 4, 2011

crankywanker said:
my voltage meter slowly dropped down from 14-10.

I don't want to beat this to death, but, to test the ALT output, you take a reading at idle, raise the RPMs to 1500, take another reading. Any change?
Add a load by turning on the head lights and or blower motor to HI. At this point a good ALT will show about a mid 14sV charging rate. If not any of those auto stores can check it, as well. If the ALT checks out, then your battery, most likely, has a bad or weak cell and should be replaced. In any rate, if you future plans include an electric Fan setup, consider up grading to a higher ALT output, bearing in mind your wiring has to be up to the task of conducting the increased AMPs the fan will draw.
Just something to keep ion mind.
Happy Motoring!

robbz28 · Mar 4, 2011

That alternator should be the same....also get a new voltage regulator, they range from 15 bucks and up. In fact, it might just be the voltage regulator going bad. It is usually on the drivers side mounted beside the radiator, a little black box. But as Poppy said, AutoZone can test an alternator for you and do a load test on your battery and usually for free. I upgraded from a 24 amp alternator to a 65 and had no problems, just make sure you get a new voltage regulator. I made the mistake of not replacing my regulator and it failed and sent a huge amount of juice to my battery, thus making my battery get hot and leak battery acid all over my chrome engine components

grainboy · Mar 14, 2011

I ran into the same problem when I installed my electric fan. I bought an externally regulated 100 amp alt off ebay for about 100. even came with a new regulator.

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