Stock 1993 charging issue at idle

[Charlie1]

104k all stock 1993 5.0 5 speed. Has a new alternator, new battery, no under drive pulleys. Car charges fine with no accessories on, around 14.2 volts at the battery. As soon as the headlights are turned on the voltage slowly drops down into the 12’s unless I rev up the engine. I’ve tried three new 75 amp alternators and several new batteries over the years, even added an overdrive smaller alternator pulley. All the ground cables are clean and tight as well as the positive cable. It can be the blower motor instead of the headlights and the voltage slowly drops, the more accessories the faster the drop. At night I’ve always been able to see the lights dim when setting in traffic and brighten as soon as throttle is applied. This car has been in our family since it was new and it has always done this as far back as I can remember. Any suggestions?

 

[gkomo]

The stock alternators were never very good. Sounds like it’s time to do the 130amp alternator upgrade (many kits out there for this) as it’s a very common upgrade.

 

[Charlie1]

That’s on the lines of what I’ve been reading, meanwhile I upped my rpm to 850 or so using the idle reset procedure, it’s a bit better but the 130 is my only option and a quite popular one. Thanks

 

[nickyb]

Once you go 3g you never go back.

 

[Charlie1]

Once you go 3g you never go back.

I couldn’t imagine running electric fans off this 2G alternator lol, at least with the 3G I’d be able to

 

[AeroCoupe]

I’m not saying it’s the issue but have you replaced the alternator wiring harness? I only say this as the wires can corrode internally (turn green) and will cause all kinds of issues. To test this remove the connection at the alternator that has the black/orange wires and where they attach at the starter solenoid and ohm them. They should be near zero ohms as short as they are. If you get a high resistance my guess would be they need to be replaced. Someone correct me here if I’m wrong.

This is a good thread on trouble shooting the 2G and 3G alternators specifically jrichker’s post which is the second post in the thread:

Thread 'Voltage regulator/alternator problems'

Nov 12, 2018

My alternator on my 1991 wont charge my battery, I replaced the battery and the alternator, still wont get charge. I pulled the cluster and found that the ribbons that go to my battery Indicator lamp are a little bashed up. Does anybody know how I can repair those ribbons? Or is there a way to bypass my cluster at the voltage regulator or at the harness behind the cluster? Or is there another problem that I'm overlooking, thanks!

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• alternator fox foxbody help problems voltage regulator
• Replies: 2
• Forum: Fox 5.0 Mustang Tech

If you want to keep the car stock then Ron Francis makes a new harness but you have to get the headlight harness as the alternator wiring is in this harness. They also make one for the 3G/4G alternator. Neither is cheap ($200+) but it retains the factory look.

If you don’t care about it being factory stock then you could look at replacing the fusible link and the two black/orange wires and see if that corrects the issue. This would be a little work but you could do it outside of the headlight harness to see if it is the issue.

Installing a 3G is what I would and have done but neither of my cars are stock and I will never have a completely stock vehicle. There is a thread on here for installing a 3G but it comes back as a broken link. I’m currently in Germany so maybe it’s on my end but I messaged Noobz to take a look.

http://www.stangnet.com/mustang-forums/threads/87-93-130amp-alternator-install-how-to.870572/

Whatever you do install 4 ga ground wires from the battery to frame and from frame to the block of the motor. If you do not have adequate grounding then the higher amp alternator will not work as well.

 

[nickyb]

I gotta agree with aero either way you should upgrade your ground wires, Ford's are known for week grounds.

 

[Mustang5L5]

Once you go 3g you never go back.

6G alternator