Nabster

I want to upgrade my stock alternator, I'm thinking to a 100 amp or so. I don't really want to go to a 1 wire setup. I get a bit of headlight dimming at idle compared to on throttle, and I've got some other small electrical changes to the system so I think I'm justified in wanting this upgrade. All my searching turns up little bits and pieces of information, but nothing that's a straight answer to my questions.

Assuming I go with a 3 wire alternator (because I don't really want to do a 1 wire setup- I'm trying to avoid the whole issue with them not automatically charging and the alternator gauge not working with them):

1) Is it a simple remove and replace to go from the stock alternator to a 100 amp (or 130, whatever it is they come in)?

2) I don't want chrome or any special finish, just a basic "as cast" finish or whatever it's called. Should this sort of alternator be available at a parts shop, or do I need to special order it?

3) Do I need to upgrade any wiring aside from the main lead? Say I go with a 3G alternator, (I'm not completely sure what difference this is?) I understand I'll need an adapter wiring harness and new voltage regulator?

4) Do I need a different bracket for it to fit?

I think for now that covers my questions. I already have some partial answers to these, but as I mentioned my searches gave me partial and conflicting answers about some aspects, so I'm hoping to clear those up with this.

Thanks!

chris66dad

This is what I have and it works great. Seller (John) was great. Call him directly for a better price.
http://cgi.ebay.com/ebaymotors/POLIS...d=p3911.c0.m14

It is plug and play with no wiring changes
You will need a dual V belt pully. My single would slip and squeal under high loads
Here is the pully from same vendor:
http://cgi.ebay.com/ebaymotors/CHROM...=p3911.c0.m144

Uses same bracket.

But...
It is Polished and is VERY noticeable when you pop the hood. But that is a GOOD thing!

Good Luck and BE Safe

MetalEd

If your battery is getting a charge and not ending up dead, you may want to check out this solution. Upgrading your alternator might not fix your headlight problem.
Have you upgraded your lights to run off a relay yet? The older wires, switches and such can cause your lights to dim even if you upgrade the alternator. It's a problem for a lot of older mustangs that have plenty of alternator output to run everything. (corrosion and the actual circuit size draws too much current away from the headlights. A relay allows the headlights to draw power from the power source.)
The relay is simple to do and there are instructions here and with kits you can buy, to use your existing switches/wiring to trigger the relay and then connect the headlights direct to your charging system/battery so it gets the amps they need. Mustang specific Kits are the best way to go since they are almost plug-and-play, without altering or cutting your stock wiring, just adding a some new relays and plug in the wiring. The have the correct connectors so you don't have to worry about cutting wires.
Especially if you upgrade your headlights to higher wattage of modern Halogen/Xenon HID bulbs, your stock wiring/circuits might not be able to handle them. This would help your "dimming headlights" even after an alternator upgrade.

Here's a thread that covered both the alternator and headlight wiring problem you are talking about:

https://mustangforums.com/forum/clas...rpms-drop.html

Starfury

I agree. You don't really need to look at an alternator upgrade unless you're running a large sound system or lights that will set things on fire. The stock alternator will power a standard stereo and all of the electrical in the car with no problems, assuming your wiring is in good shape. However, your wiring is probably in poor shape after 40 years, so I'd look at that first.

Keep in mind, most alternators aren't going to put out much power at idle. I have the exact same problem you have with dimming lights at idle, but who really cares? The battery gets charged and the lights don't dim when I'm driving around, which is the important thing.

chris66dad

Relays definitely helped me. I switched to halogen bulbs and the old wiring was not passing the required current. I am also running halogen driving lights on a separate relay circuit. I am using an electric fan and plan to add a large stereo soon. The alternator upgrade was a "must do" for me.
At night with the hi beams and driving lights on and the electric fan running, my lights do dim slightly at idle.

Nabster

This is the problem I was hoping to avoid. The wiring is fine, the slight dimming of my lights at idle shows me the alternator isn't pushing out quite enough power for my tastes. The battery is good, at idle the system charges at under 14 volts, on throttle it charges mid 14 volts as it should. Voltage regulator is new and electronic, it's not part of the problem

I've got a modern higher power stereo (with a couple extras that also draw power) with modern speakers and will be installing another pair up front next year. The headlight bulbs are the stock sealed halogen type.

I don't want to install relays for the headlights because I don't want to be running a bunch of new wires (I've done all sorts of relays and headlight wiring for HID lights on my other car so I know how it all works)- it looks really off compared to the rest of the engine bay. This is also the reason I don't want a shiny alternator as suggested, you say it looks good, but the simple answer is that it doesn't- it does not go with the rest of my engine bay. Now, if I had a proper shop area and could pull the engine and do everything in the engine bay properly, I'd have no problem installing relays because I could redo all the wiring with new wires and then bundle them up and hide them properly, but because I don't have the proper space or access to do all that I'm not going to do a halfway job.

I don't want to sound rude or mean here, but I'd just like some answers to my questions, not suggestions to add a bunch of stuff and change how it all works- that's what I'm trying to avoid. Hopefully you can see what I mean, I'm trying to keep this as period and original as possible, adding a bunch of shiny crap and relays is the wrong direction I'm going with with this car.

For someone in another situation your advice is good and would work quite well, but for me, it's not what I'm looking for- I mean I could tell you all to swap out your engines for modern smaller and more efficient ones because they would do the job too, but it probably wouldn't be what you want.

2+2GT

The dimming at idle is not caused by a lame alternator. It's likely a 500 amp alternator would do this. It's caused by the alternator turning too slowly to operate. The alternator puts out about 14.2V when regulated properly, but the battery is only 12V. Installing a smaller pulley would cure the problem at a fraction of the cost of swapping the alternator out (or just turning the idle screw for a faster idle). Dimming lights at idle was normal, especially with the 289 High Performance, BOSS 302, BOSS 429, and BOSS 351, because they had an oversize pulley to prevent overspeeding the alternator at high engine speeds.

chris66dad

I answered 3 out of 4 of your questions with my first post.

The link I gave for Ebay dealer will have a 100 amp 3g cast casing unit

Apologies for going on a tangent and hijacking your thread.