Will a Higher Amp Alternator Require Wiring Upgrade? - Vintage Mustang Forums
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post #1 of 7 (permalink) Old 06-19-2019, 02:24 PM Thread Starter
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Will a Higher Amp Alternator Require Wiring Upgrade?

Having Charging issues on my Stock 66 289 2V Auto Fastback.
Considering upgrading to a Higher Amperage Alternator.
Wondering how high of an upgrade over Stock Amperage Alternator would require heavier gauge wires.
At least to the Voltage Regulator...
Anyone have to deal with or research this before?
Thank you,
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post #2 of 7 (permalink) Old 06-19-2019, 02:43 PM
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How much amperage? Mainly it’s the charge wire from the alternator to the battery that you need to upgrade to carry the juice. 75 amp? I’d use 8 gauge. 100-120 amp? 6 gauge. More than that 4 gauge. Use quality wire, a lot of stuff I see anymore is aluminum that is copper coated, that won’t carry as much current. I know some will say bigger gauge but it’s such a short run those sizes in a quality wire will carry the current. When you get at the hundred range you’ll want a fuse (mega type) for protection.
As for charging issues, do you have a lot of accessories added? Maybe just the components you have could use a refresh or replacement.

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post #3 of 7 (permalink) Old 06-19-2019, 03:27 PM
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Unless you have a bunch of high-draw accessories, there's no need for more than the factory "heavy duty" charging system. Most charging issues can be traced to bad grounding, poor connections and wiring that has been butchered by the PO. Get a top quality electronic regulator from Standard or Motorcraft, not one of the "correct" repops that are all looks and don't work right. Check, repair and clean all of your wiring and connections. Replacement alternator harnesses are under $30 from any Mustang vendor. Verify that you have a solid battery to chassis to engine ground path. IIRC, there's a ground strap on the 66 from the upper starter bolt to the firewall - if that's missing it'll cause all sorts of issues.

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post #4 of 7 (permalink) Old 06-19-2019, 04:36 PM Thread Starter
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Thank you for the reply, I just got the car a few months ago.
Recently put in a new battery but have been having to keep putting that on a charger.
When I've run it at night the headlights seem to be dim at low idle (stop signs).
The headlights are regular, not Halogen, and it has the original AM radio with a single dash speaker.
No added accessories yet, but would like to be able to charge the cell phone.
Just received a 70 Amp Alternator from NPD, when I opened the box there was an insert caution notice about wiring.
I hadn't even considered that when I ordered the higher Amp unit (my bad).
I'm still working the bugs out of this Pony.
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post #5 of 7 (permalink) Old 06-19-2019, 04:42 PM
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usually the charge wire is upgraded as a matter of course. a 10 gauge wire will do nicely for most applications.

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post #6 of 7 (permalink) Old 06-19-2019, 05:03 PM Thread Starter
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To add to my second post, I did find a mess in the wiring under the dash, spliced & cut wires which I cleaned up and redid as best I could follow wiring diagrams found online. Also replaced the Headlight switch, got all the Dash & Courtesy Lights working (except for the AM Radio). The fuse box connections were corroded, cleaned those up, but probably ought to replace that also. Will have to check when I get home tonight for the Ground Strap to the Firewall, will get one of those if it's missing.
Thank you for all the feedback, will post findings and results later!

I corrected the bad splices and open ended cut wires shown in the attached picture here.
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post #7 of 7 (permalink) Old 06-19-2019, 09:27 PM
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Yes. It will, but not the wiring... You have to upgrade the Voltage Regulator underhood to a 1980-'s-Early 90's type Motorcraft Electronic Solid State Unit... and you are good to go..

Take your pick...




You can also use Compatible VR's made by Standard Motor Parts..... But use no other brands other than Standard Motor Parts or Original Motorcraft. All the rest are JUNK...with a capital "J"...


Have fun..

Happy Motoring...

Tony K.
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File Type: jpg Motorcraft Electronic Solid State regulator-1.jpg (88.2 KB, 3 views)
File Type: jpg Motorcraft FOPZ10316A-ANG (GR-540B).jpg (26.2 KB, 25 views)

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