High Amp Alternators for older GM's
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The factory 63 Amp alternator in my 1973 Buick Electra was in dire need of replacement - it was old, and quietly putting out much less than it's rated output. Taxing it with a bigger stereo, the new rear window defogger, and aftermarket halogen headlights sealed it's fate. It needed to go away and be replaced with something that was up to the task I had placed before it. This article is based on my experience in doing that work. I hope that it helps you if you attempt this on your own car. As always, this is for informational purposes only and no warranty is expressed or implied. Do this at your own risk. Use common sense. If you fry yourself or your car, it's not my fault.

After much hunting, I discovered that there is a commonly available version of the GM internally-regulated alternator that's rated at 94 amps - the biggest factory units that are commonly known to be available were rated at only 63 amps. The case on the 94 amp unit is identical to the one that came in almost every GM vehicle from about 1972 through 1983, and it is dimensionally similar to the externally regulated units used from 1963 through about 1972. This special 94 amp alternator is even stocked by most auto-parts stores and retails for only a bit more than the 63 amp version - about $80! When I found that out, I scarfed one up, and dropped it into the car. Sure enough, it worked like a charm. It put out a good amount of amperage at idle (unlike most high amp conversion kits which actually put out less at idle than the factory unit!), fit right into the factory space, and did not generate much more heat than the 63 amp unit. This is critical for the alternator to live any length of time in a tight mounting location, as it is in my car.

The first caveat is that you may need to re-clock the front and rear case halves on the 94 amp unit so the brackets and electrical plugs line up on your application. It's as easy as removing the four case screws and gently rotating the back of the unit relative to the front of the unit until it looks like your original alternator, and then re-installing the screws. This is easy, but it may void any warranty on the 94 amp unit, so do it at your own risk. (Making friends with the parts guys at your local automotive supply store is a good place to start. Around here, they know me quite well at B&B Auto Parts - so much that most of the guys recognize my voice on the phone and just say "Hi Mike! What car?". Scary, but true.) Anyway, the part # on the 94 amp unit I got is #1105541. Your local parts store should be able to cross reference this number into the particular brand of rebuild alternator they stock - in my case it referenced down to an AllStar part number of 7294-9, where the -9 indicates the 9 o'clock clocking position. (I recently found out that you can also get a -6 unit with a 6 o'clock position if you feel like ordering it instead of re-clocking it yourself.)

The only warning is about the size (gauge) of the main wire that carries the power from the alternator to where it hooks up to the larger battery cable and then out to the rest of the cars electrical system. This wire must be large enough to handle the maximum possible output of the alternator - you should check out my Wire Capacity Chart for more information. In my case, the existing 10 gauge wire was marginal at best for the new 93 amp alternator, and will be replaced with a new 8 gauge (or larger) wire at a later date. For now, it's there and working, but I have to be very careful to not get the car into a situation where the alternator will go to max charging. (For example, this means if I have to jump the car, I give the battery extra time to charge before I try to start the car so the alternator doesn't try to put 93 amps into the battery at initial startup...) Most GM's I've looked into use a 10 gauge wire for the alternator to battery cable connection (mine did), so be sure to check the manual for your car to find out the size of the wire, and if in doubt - replace it. In a peak power situation you're going to be pumping a lot more current through this wire, and if it's too small or has bad insulation, well, at best it could to be a long walk to the nearest phone booth and at worst it could to be the start of a nasty fire under your hood. Neither is very good or fun, so be smart, do the job right, and be safe.

 

If you want to install this unit in an older 1963-1970 GM vehicle that originally used an externally regulated alternator, you will need to do some wiring work or use a conversion kit available from various sources, but the mounting brackets should line right up. Since wiring is much easier to fix than the brackets, that sounds like a good deal to me. I have a tech article about Alternator Conversions for GM's that has some very good details on this if you're interested.

 

Aside from replacing the charging wire with a larger one if you need to, the actual installation of these higher amp alternators is identical to the factory process for replacing the existing alternator. Remove the old one and disconnect the wires, then bolt the new one in and re-connect the wires. The mounting points and wire connections will be the same, and the physical size of the new alternator is pretty much identical to the original unit. Consult the manual for your vehicle for the exact process if needed but it should be one of those "self-explanatory" things once you get started.


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Page last updated 01/02/2009 01:51:39 PM